EXPERIMENTAL  POLLINATION 


AN  OUTLINE  OF  THE 


ECOLOGY  OF  FLOWERS  AND  INSECTS 


BY 


Frederic  E.  Clements  and  Frances  L.  Long 


QK926      | 

Q  £  Published  by  the  Carnegie  Institution  op  Washington 

Washington,  1923 


Oty*  B.  31  Mi  ffitbrara 


Nortlt  (Carolina  &tatp  Inineraitij 


olina  State  Library 


^["CAROLINA  STATE  UNIVERSITY  L 


THIS  BOOK  IS  DUE  ON  THE  DATE 
INDICATED  BELOW  AND  IS  SUB- 
IECT  TO  AN  OVERDUE  FINE  AS 
POSTED  AT  THE  CIRCULATION 
DESK. 


19  1980 


MAY 


/yyy 


CLEMENTS    &    LONG 


Edith  S.  Clements  I 


Painted  flowers  of  Aconitum  and  Delphinium,  showing 
the  method  of  experiment. 


North  Ca(J$i*  S'aLe  Library 
#      Raleigh 

EXPERIMENTAL  POLLINATION 


AN  OUTLINE  OF  THE 

ECOLOGY  OF  FLOWERS  AND  INSECTS 


BY 


.aca 


Frederic  E.  Clements  and  Frances  L.  Long 


North  Q£M!ina  State  Librarv 

Published  by  the  Carnegie  Institution  of  Washington 
Washington,  1923 


CARNEGIE  INSTITUTION  OF  WASHINGTON 
Publication  No.  336 


Copies  of  this  feoek 
NOV  6    1923 


CONTENTS. 


1.  Introduction  and  Methods 

Introduction 

Objectives 

Methods 

General  principles 

Normal  pollination 

Experimental  pollination 

Organization  of  experiments 

Change  of  position  or  place 

Concealing  or  disguising  flowers. . 

Mutilation 

Artificial  and  painted  flowers .... 
Addition  of  parts  or  substances . . 

Competition 

Manipulation  of  insects 

Life-history  methods  and  records . 
Life-history  record  of  a  represen- 
tative species 

2.  Normal    and    Experimental    Pol- 

lination   

Aconitum  columbianum 


Page 
3 
3 
4 
4 
4 
6 
6 
7 
7 


Normal  pollination 15 

Structure 

Behavior 

Experiments 

Change  of  position 

Horizontal  racemes 

Racemes  inverted 

Mutilations 


15 
15 
1(3 
16 
16 
16 
17 

Cotton  plugs 17 

Stamens  removed 17 

Hood  split 17 

Hood  removed 17 

Hood  and  nectaries  removed       17 

Lower  sepals  removed 17 

Side  petals  removed 18 

Competitive  relations 18 

Artificial  and  painted  flowers. .        18 

Normal  colors 18 

Artificial  flowers 19 

Painted  flowers 20 

Addition  of  honey  and  odor. .  .       21 

Honey 21 

Perfumes 22 

Summary 22 

Delphinium   scopulorum 22 

Normal  pollination 22 

Habit  and  structure 22 

Behavior 22 

Experiments 23 

Change  of  position 23 

Inverted  racemes 23 

Horizontal  racemes 23 

Mutilation 23 

Cotton  plugs 23 

Petals  removed 23 

Spur  removed 23 

Landing-platform  removed. .        24 
Artificial  and  painted  flowers . .        24 

Crepe-paper  corollas 24 

Crepe-paper     corollas     with 

spurs 24 

Painted  flowers 25 


2.  Normal    and    Experimental    Pol- 
lination {Continued). 
Delphinium  scopulorum  (Continued). 

Addition  of  odor 

Perfume 

Summary 

Rubus  deliciosus 

Normal  pollination 

Habit  and  structure 

Behavior 

Variation  in  visits 

Experiments 

Mutilation 

Petals  split  or  shortened .... 

Stamens  covered 

Artificial  and  painted  flowers . . 

Crepe-paper  corollas 

Painted  corollas 

Addition  of  honey  or  odor .... 

Honey 

Summary 

Rubus  strigosus 

Normal  pollination 

Habit  and  structure 

Behavior 

Experiments 

Mutilation 

Floral  envelopes  or  stamens 

removed 

Rosa  acicularis 

Normal  pollination 

Habit  and  structure 

Behavior 

Experiments 

Mutilation 

Corolla  shortened 

Stamens  masked 

Artificial  and  painted  flowers . . 

Crepe-paper  corollas 

Addition  of  honey  and  odor. .  . 

Honey 

Honey  and  talcum  powder. . 

Camphor 

Summary 

Geranium  caespitosum 

Normal  pollination 

Habit  and  structure 

Behavior 

Calendars 

Experiments 

Change  of  position 

Flowers  vertical  or  inverted 

Mutilation 

Cotton  over  nectaries 

Excision 

Artificial  and  painted  flowers. . 

Crepe-paper  corollas 

Addition  of  honey  and  odor.  .  . 

Honey 

Summary 

Chamaenerium  angustifolium 

Normal  pollination 

Habit  and  structure 


25 
25 
26 
26 
26 
26 
26 
27 
29 
29 
29 
29 
30 
30 
30 
31 
31 
31 
32 
32 
32 
32 
33 
33 

33 
33 
33 
33 
33 
34 
34 
34 
35 
35 
35 
36 


IV 


CONTENTS 


Page 
2.  Normal   and    Experimental    Pol- 
lination (Continued). 
Chamaenerium  angustifolium  (Cont.). 

Behavior 45 

Experiments 48 

Change  of  position 48 

Racemes  inverted 48 

Mutilation 48 

Floral  envelopes  removed.  . .  48 
Upper    petals    and    the    in- 
cluded sepal  removed ....  49 
Stamens  and  style  removed .  49 
Artificial  and  painted  flowers. .  51 

Crepe-paper  corollas 51 

Painted  corollas 51 

Addition  of  honey  and  odor. .  .  52 

Honey 52 

Odor 52 

Perfumes 53 

Flavoring  extracts 53 

Summary 54 

Pachylophus  caespitosus 54 

Normal  pollination 54 

Habit  and  structure 54 

Behavior 55 

Experiments 56 

Artificial  flowers 56 

Crepe-paper  flowers 56 

Petals  obscured 56 

Mentzelia  multiflora 56 

Normal  pollination 56 

Habit  and  structure 56 

Experiments 56 

Crepe-paper  flowers  and  com- 
petition    57 

Crepe-paper  corollas 57 

Summary 58 

Frasera  speciosa 58 

Normal  pollination 58 

Habit  and  structure 58 

Behavior 58 

Experiments 59 

Mutilation 59 

Types 59 

Artificial  and  painted  flowers. .  59 

Crepe-paper  corollas 59 

Painted  corollas 60 

False  corollas 61 

Addition  of  nectar  and  odor. . .  61 

Nectar 61 

Summary 61 

Mertensia  pratensis 62 

Normal  pollination 62 

Behavior 62 

Experiments 63 

Mutilation 63 

Changes  of  corolla 63 

Castilleia  miniata 63 

Normal  pollination 63 

Habit  and  structure 63 

Behavior 63 

Experiments 64 

Mutilation 64 

Upper  lip  removed,  spike  in- 
verted    64 

Painted  flowers 64 

Painted  bracts 64 


Page 
2.  Normal    and    Experimental    Pol- 
lination (Continued). 

Pentstemon  glaber 65 

Normal  pollination 65 

Habit  and  structure 65 

Behavior 65 

Calendars 66 

Experiments 68 

Change  of  position 68 

Racemes  inverted 68 

Racemes  horizontal 70 

Mutilation 70 

Cotton  at  the  corolla  mouth.  70 
Styles,  stamens,  and   stami- 

node  removed 70 

Corolla  split 70 

Corolla    lips    separated    and 

staminode  raised 71 

Upper   lip    removed    at   the 

throat 71 

Lower  lip  shortened  half. ...  71 

Lower  lip  removed 71 

Lower  lip   and   part  of   the 

tube  removed 71 

Lips   removed   except  lower 

lobe 71 

Corolla  tube  shortened  half.  71 

Petals  separated 71 

Lower    lip    split    into    three 

petals 71 

Tube  end  of  a  corolla  slipped 

over  the  staminode 72 

Comparative  relations 72 

Artificial  and  painted  flowers. . .  72 

Crepe-paper  corollas 72 

Corolla  painted  with  water- 
colors 72 

Honey  and  odor 72 

Sirup  added 72 

Pentstemon  gracilis 73 

Normal  pollination 73 

Habit  and  structure 73 

Behavior 73 

Calendars 74 

Experiments 75 

Change  of  position 75 

Racemes  inverted 75 

Racemes  horizontal 75 

Mutilation 75 

Landing-platform  removed. .  75 
Brush  of  staminode  removed  75 
Anthers  and  recurved  por- 
tion of  upper  lip  removed  75 
Upper  lip  partly  removed.  .  75 
Lobes  of  upper  lip  separated  75 

Petals  split  to  the  base 76 

Pentstemon  glaucus 76 

Normal  pollination 76 

Normal  behavior 76 

Experiments 76 

Mutilation 76 

Upper  lobes  split  to  base ...  76 

Lower  lip  removed 76 

Outer  lobes  of  lower  lip  re- 
moved    76 

Staminode  removed 76 


CONTENTS 


Page 

2.  Normal    and   Experimental    Pol- 

lination (Continued). 
Pentstemon  glaucus  (Cont.). 

Middle  lobe  of  the  lower  lip 

removed 77 

Upper  lip  removed 77 

Pentstemon  secundiflorus 77 

Normal  pollination 77 

Behavior 77 

Calendar 77 

Experiments 77 

Odor 77 

Powders  and  extracts 77 

Cotton  wads  sprinkled  with 

peppermint 78 

Summary 78 

Monarda  fistulosa 79 

Normal  pollination 79 

Habit  and  structure 79 

Behavior 79 

Experiments 80 

Mutilation  and  competition.  .  .  80 

Plan 80 

Summary 88 

Resume 89 

Variation  in  number  of  visits. ...  89 

Changes  of  position 90 

Masking  with  cotton 90 

Mutilation 91 

Artificial  flowers 92 

Painted  flowers 92 

Honey  and  odor 93 

3.  Competition  and  Constancy 94 

Significance 94 

Competition 94 

General  plan 94 

Rubus  strigosus 95 

General  relations 95 

Rubus  strigosus  and  Rubus  deliciosus  95 

Comparison 95 

Experiments 95 

Summary 97 

Rubus  strigosus  and  Rubus  deliciosus  97 

Comparison 99 

Summary 99 

Competition  of  Rubus  with  Frasera, 

Cleome,  etc 99 

Comparison 97 

Experiments 99 

Summary 99 

Rubus  strigosus  and   two  or  more 

competitors 99 

Comparison 99 

Summary 100 

Rubus  deliciosus 101 

Experiments 101 

Summary 101 

Rosa  acicularis 101 

Comparison 101 

Experiments 102 

Summary 102 

Competition    with    normal    and 

mutilated  Aquilegia 105 

Geranium 105 

Comparison 105 

Experiments 106 

Summary 109 


Page 

3.  Competition  and  Constancy  (Con- 

tinued) . 

Chamaenerium  angustifolium 110 

Comparison HO 

Experiments HO 

Summary HO 

Pentstemon HO 

Comparison HO 

Experiments 113 

Summary 113 

Monarda  fistulosa 115 

Comparison H5 

Experiments 115 

Summary 115 

Weight  and  composition  of  pollen 

loads 119 

Value  and  methods 119 

Discussion 127 

Constancy 128 

Definitions 128 

Early  observations  of  constancy  129 

Bennett's  studies  of  constancy  130 
Christy's  studies  of  methodic 

habits 130 

Mueller's  results 130 

Bulman's  studies 131 

Ord's  conclusions 131. 

Plateau  and  Perez 131 

Constancy  in  Bombus 132 

Lovell's  conclusions 132 

Kranichfeld's  observations 133 

Origin  of  oligotropism 133 

Resume 134 

Experimental   results   in   compe- 
tition   134 

Effects  of  competition 134 

Constancy   as   shown    by   pollen 

loads 135 

4.  Principles  and  Conclusions 136 

Introductory 136 

Early  experiments  of  Plateau  and 

others 136 

Artificial  flowers 136 

Nectaries 137 

Color  sense  of  bees 138 

Response  to  detached  petals.  ...  139 
Color    preferences    of    nocturnal 

moths 140 

Response  to  color  without  anten- 
nae  '. 140 

Perception  of  form 140 

Response  of  wasps  to  color 143 

Response  of  wasps  to  odor 145 

Main  researches  of  Plateau 145 

Masked  flowers 145 

Removal  of  corolla 147 

Response  to  different  colors 148 

Addition  of  honey  to  vivid  nectar- 
less  flowers 149 

Anemophilous  flowers 150 

Entomophilous    flowers    of    dull 

color 150 

Artificial  flowers,  second  series .  .  .  150 

Artificial  flowers  of  green  leaves .  .  151 

Conclusions  as  to  artificial  flowers  152 

General  summary 152 

Role  of  vexillary  organs 153 


VI 


CONTENTS 


Page 
4.  Principles  and  Conclusions  {Con- 
tinued), 
Main   researches   of   Plateau  (Con- 
tinued). 

Choice  of  colors  by  insects 154 

Errors  made  by  Anthidium 155 

Admiration  of  syrphids  for  bright 

flowers 156 

Attraction  of  colored  cloths  and 

brilliant  objects 156 

Constancy  among  bees 157 

Mistakes  made  by  bees 157 

Removal  of  the  antennae  of  bum- 
ble-bees       158 

Evidence  of  the  attractive  role  of 

odor 159 

Decorollate    poppies    and    insect 

visits 159 

New  experiments  with  artificial 

flowers 160 

Conclusions  as  to  artificial  flowers     162 
Macroglossa  and  false  flowers.  ...      164 
Entomophilous  flowers  little  vis- 
ited by  insects 165 

Related  studies  and  critiques 166 

Comparative  importance  of  odor 

and  color 166 

Perez's  critique  of  Plateau's  work     167 

Effect  of  colors  at  the  hive 168 

Critiques  of  Kienitz-Gerloff 168 

Knuth's  critique 169 

Reeker's  experiments  with   arti- 
ficial flowers 171 

Decorollate  poppies 171 

Response  to  color  and  odor  by  a 

hawk-moth 175 

Vexillary  nature  of  the  plume  in 

Muscari 175 

Forel's  experiments  with  covered 
dahlias  and  with  artefacts ....      176 

Response  of  Syritta 178 

Andreae's  experiments  with  arti- 
ficial flowers 178 

Andreae's    conclusions 181 

Andreae's  criticisms  of  Plateau's 

work 182 

Plateau's  criticisms  of  Andreae's 

work 182 

Wery's  experiments  with  decorol- 
late and  artificial  flowers 183 

Plateau's    criticisms    of    Wery's 

experiments 185 

Experiments   of    Weismann    and 

Errera 186 

Orientation  of  the  honey-bee  at 

flowers  of  the  same  species ....      186 
Discrimination    between    similar 

species  of  flowers 187 

Orientation  of  the  bee  within  the 

flower 188 

Chance  observations  of  visits   to 

imitations 189 

Knoll's     critique     of     Plateau's 

study   of   Macroglossa 193 

Recent  investigations 193 

The  color  sense  of  the  honey-bee     193 
Can  bees  distinguish  colors? ....      194 


Page 
4.  Principles  and  Conclusions  (Con- 
tinued) . 
Recent  investigations  (Continued). 

The  pollination  of  green  flowers .  .      195 
Conspicuous  flowers  rarely  visited 

by  insects 196 

Response  of  honey-bees  to  colored 

artefacts 197 

Pattern  vision  in  the  honey-bee. .      198 
Experiments    with    cotton    blos- 
soms       198 

Color  sense  and  memory  in  the 

honey-bee 199 

Frisch's  researches — sense  of  color 

and  form  in  the  honey-bee ....     200 
The  supposed  color  sense  of  the 

honey-bee 201 

Seasonal  changes  in  response  to 

honey 202 

The  sense  of  smell  in  the  honey- 
bee       203 

Bombylius    and    the    colors    of 

flowers 205 

Vision    and    flower    behavior    of 

Macroglossa  stellatarum 206 

Response  of  bees  to  spectral  bands     207 
Evaluation  of  Plateau's  researches     208 

Forel's  estimate 208 

Contradictory  nature  of  Plateau's 

later  conclusions 212 

Conclusions  as  to  Plateau's  views     213 

Senses  of  insects 213 

Sight 213 

The  mosaic  theory 213 

Criticisms  of  Plateau's  views  as 

to  vision 215 

Sensibility  to  color 215 

Perception  of  form  and  move- 
ment by  insects 215 

Discrimination  of  form 216 

Vision  in  honey-bees 216 

Vision  in  ants 217 

The  role  of  ultra-violet  in  at- 
traction      217 

The  homing  faculty  in  bees  and 

wasps 217 

Fabre's    experiment  with   bees 

and  wasps 217 

Lubbock's  and  Forel's  critique 

of  Fabre's  conclusions 218 

Homing  faculty  of  bees 220 

Sense  of  direction  in  ground- 
wasps 220 

Disturbance     of     memory     in 

wasps 221 

Observations  on  the  homing  of 

Bembex  and  Pampilus 221 

Memory  of  place  in  Osmia.  .  .  .     222 
The  field  and  nest  flights  of  the 

bumble-bee 223 

The  homing  of  the  mud-dauber 

wasp 223 

Experiments  on  the  orientation 

of  bees  in  homing 224 

Homing  abilitv  in  Polistes ....      224 
Smell 225 


CONTENTS 


Vll 


Page 
4.  Principles  and  Conclusions  (Con- 
tinued). 
Smell  (Continued) . 

Sense  of  smell  in  insects  de- 
prived of  antennae 225 

Forel's  criticisms  of  Graber's 
results 226 

Hauser's  experiments 227 

Olfactory  pores 228 

Experiments  with  antennse 
removed,  mutilated,  or 
coated 228 

Experiments  with  wings,  legs, 

and   stings   mutilated 229 

Mclndoo's  experiments  with 
deantennate    insects 229 

Present  status  as  to  the  seat  of 
the  olfactory  sense 230 

Intelligence 232 

Relation  between  the  senses 
and  mental  faculties  of  in- 
sects      232 

Memory  and  general  intelli- 
gence of  wasps 233 

Memory  of  place  in  bees 233 

Memory  of  time  and  asso- 
ciation of  impressions.  .....      235 

Memory  of  time  and  memory 
association  in  honey-bees.  .  .     236 

Intelligence  of  honey-bees.  .  .  .     236 

The  psychic  powers  of  insects     237 


Page 

4.  Principles  and  Conclusions  (Con- 

tinued). 

General  resumS 238 

Treatment 238 

Attraction 238 

Color 238 

Mutilation 238 

Artificial  flowers 239 

Painted  flowers 240 

Inclosing  flowers  in  glass 241 

Green  flowers  and  showy  nec- 

tarless  flowers 241 

Color  preference 241 

Odor 244 

Masking    or    covering    flowers 

to  conceal  color 244 

Odor  of  honey 244 

Effect  of  added  odors 245 

Relative    value    of    color    and 

odor 245 

Form 245 

Distinction  and  role 245 

Attraction  at  a  distance  and  near 

at  hand 246 

Learning  and  habit 247 

Memory  and  intelligence 247 

5.  Pollinators  and  Flowers  Visited 249 

6.  Flowers  and  their  Visitors 256 

Bibliography 268 

Index 273 

Description  of  Plates 276 


EXPERIMENTAL  POLLINATION 

AN  OUTLINE  OF  THE 
ECOLOGY  OF  FLOWERS  AND  INSECTS 


BY 

Frederic  E.  Clements  and  Frances  L.  Long 


LIST  OF  PLATES. 

Plate  Page 

1.  Painted  flowers  of  Aeonitum  and  Delphinium Frontispiece 

2.  Life-history  of  the  flowers  of  Aeonitum  columbianum  and  Delphinium  scopulorum,  272 

3.  Life-history  of  Rubus  strigosus  and  Potentilla  gracilis 272 

4.  Life-history  of  Heracleum  lanatum  and  Sedum  stenopelatum 272 

5.  Life-history  of  Galium  boreale  and  Saxifraga  bronchialis 272 

6.  Life-history  of  Campanula  rotundifolia  and  Erysimum  asperum 272 

7.  Life-history  of  Geranium  caespitosum  and  Dodecatheon  meadia 272 

8.  Life-history  of  Chamaenerium  angustijolium 273 

9.  Life-history  of  Pachylophus  caespitosus 273 

10.  Life-history  of  Pirola  elliptica,  Frasera  speciosa,  and  Gentiana  amarella 273 

11.  Life-history  of  Gilia  aggregata  and  pinnatifida,  Mertensia  sibirica,  and  Lithosper- 

mum  multiflorum 273 

12.  Life-history  of  Pentstemon  glaber 273 

13.  Life-history  of  Castilleia  miniata  and  Monarda  fistulosa 273 

14.  Life-history  of  Allium  cernuum  and  Zygadenus  elegans 274 

15.  Mutilated  and  inverted  flowers  of  Aeonitum 274 

16.  Mutilated  flowers  of  Aeonitum,  Delphinium,  and  Monarda 274 

17.  Mutilated  flowers  of  Geranium,  Chamaenerium,  and   Pentstemon  glaber 274 

2 


1.  INTRODUCTION  AND  METHODS. 

INTRODUCTION. 

The  original  plan  for  the  development  of  quantitative  ecology  con- 
templated two  series  of  monographs,  one  dealing  with  the  plant  in  its 
vegetative  relations,  the  other  in  its  reproductive  aspects.  The  first  has 
received  attention  in  a  number  of  monographs,  some  of  which  deal  with 
the  individual  and  some  with  the  community,  but  the  factors  and  processes 
involved  in  the  behavior  of  the  flower  were  necessarily  somewhat  neglected 
for  a  time.  Studies  of  the  life-histories  of  flowers  were  first  begun  in  1910 
and  these  were  followed  by  observations  and  experiments  upon  the  relations 
of  flowers  and  insects.  These  served  to  disclose  the  nature  of  the  problem 
and  to  indicate  the  methods  needed  for  a  comprehensive  experimental 
attack  upon  it.  The  main  investigation  was  begun  in  1918  and  has  been 
carried  on  actively  during  the  succeeding  summers.  As  a  consequence 
the  limits  of  the  field  have  expanded  greatly  and  the  present  treatment  is 
to  be  regarded  as  a  preliminary  endeavor  to  organize  it  upon  an  adequate 
experimental  and  quantitative  basis  in  nature. 

The  study  of  the  relations  between  flowers  and  insects,  begun  effectively 
by  Kolreuter  (1761)  and  Sprengel  (1793),  underwent  an  enormous  expansion 
at  the  hands  of  Delpino  (1867),  Hildebrand  (1867),  Mueller  (1873),  Darwin 
(1876),  Kerner  (1876),  and  Knuth  (1894)  without  becoming  experimental 
in  even  a  small  degree.  The  first  investigator  to  recognize  that  the  great 
mass  of  observational  results  needed  to  be  refined  by  means  of  experimental 
methods  was  Plateau  (1877,  1895),  and  practically  all  other  experimental 
studies  have  been  a  direct  or  indirect  consequence  of  his  work.1  The  present 
investigation  constitutes  the  exception,  as  it  was  begun  with  a  different 
objective  and  with  contacts  sufficiently  slight  to  permit  an  independent 
development  of  methods.  This  was  of  especial  importance  in  view  of  the 
comprehensive  nature  of  the  plan,  as  well  as  in  affording  a  detached  view 
of  the  methods  already  employed.  This  appears  to  have  been  justified 
by  the  outcome,  not  only  in  the  matter  of  methods  but  also  with  respect  to 
results  and  conclusions.  Moreover,  the  difference  in  objectives  has  made 
it  possible  to  plan  experiments  and  interpret  results  without  a  bias  in  favor 
of  Plateau's  views  or  those  of  his  critics.  While  the  relative  values  of 
color  and  odor  in  attraction  constitute  one  of  the  most  interesting  phases  of 
the  general  problem,  they  have  too  long  held  the  center  of  the  stage  as  a 
consequence  of  Plateau's  dramatic  challenge.  However,  even  in  the  present 
case,  the  adequate  analysis  and  evaluation  of  the  work  that  has  been  done 
make  it  necessary  to  treat  attraction  as  the  paramount  theme. 

This  investigation  has  been  carried  out  at  the  Alpine  Laboratory,  which 
is  situated  at  an  altitude  of  8,500  feet  in  the  montane  forest  climax  on 
Pike's  Peak.  It  is  perhaps  unique  in  dealing  with  an  insect  fauna  in  exclu- 
sive contact  with  a  native  flora,  though  some  of  the  experiments  have 

1  Since  this  was  written,  the  admirable  monographs  of  Frisch  and  of  Knoll  have  become 
available.  These  deal  almost  exclusively  with  intensive  control  researches  into  the  response 
of  one  or  two  species  to  color,  odor,  or  form,  and  are  indispensable  to  students  of  experimental 
pollination.  While  it  is  now  impossible  to  abstract  them  as  fully  as  they  deserve,  a  general 
account  of  the  methods  and  results  will  be  found  in  Chapter  4. 

3 


4  EXPERIMENTAL   POLLINATION. 

concerned  species  that  are  probably  outside  the  normal  experience  of  the 
visitors.  Some  studies  have  also  been  made  in  the  plains  grassland  at 
the  base  of  the  range,  and  in  the  alpine  meadows  on  the  summit  of  Pike's 
Peak,  as  well  as  a  few  preliminary  ones  in  Arizona  and  California,  but  these 
are  reserved  for  the  most  part  for  a  later  treatment. 

For  the  flowers  the  nomenclature  is  that  employed  in  Clements  and 
Clements'  "Rocky  Mountain  Flowers,"  while  the  names  of  the  Lepidoptera 
are  those  found  in  Holland's  "Butterfly  Book"  and  "Moth  Book."  In  the 
other  groups  the  determinations  have  been  made  by  the  following  specialists, 
to  whom  grateful  acknowledgment  is  made:  Dr.  J.  M.  Aldrich,  Bureau  of 
Entomology,  Washington,  D.  C;  Professor  T.  D.  A.  Cockerell,  University 
of  Colorado,  Boulder,  Colorado;  Professor  C.  Howard  Curran,  University 
of  Kansas,  Lawrence,  Kansas;  Dr.  F.  E.  Lutz,  American  Museum  of  Natural 
History,  New  York;  Professor  S.  A.  Rohwer,  U.  S.  National  Museum, 
Washington,  D.  C;  Professor  0.  W.  Oestlund,  University  of  Minnesota, 
Minneapolis,  Minnesota;  Professor  M.  W.  Swenk,  University  of  Nebraska, 
Lincoln,  Nebraska;  Professor  C.  T.  Vorhies,  University  of  Arizona,  Tucson, 
Arizona;  Professor  H.  L.  Viereck,  Biological  Survey,  Washington,  D.  C. 

Objectives. — As  already  indicated,  the  primary  object  of  the  present 
investigation  is  to  place  the  study  of  the  flower  in  relation  to  its  environ- 
ment on  the  basis  of  experiment  and  measurement.  At  the  same  time  it 
is  intended  to  give  the  fullest  value  to  the  synthetic  nature  of  the  problem 
by  placing  the  chief  emphasis  upon  the  mutual  relations  of  flowers  and 
insects.  The  life-history  of  the  flower  has  been  given  greater  attention 
than  heretofore  and  it  is  felt  that  the  life-history  of  the  insect  in  the  broader 
ecological  sense  must  receive  similar  study.  The  central  theme  is  attraction 
and  the  behavior  of  the  insect  at  the  flower,  and  in  spite  of  the  work  already 
done,  this  offers  an  enormous  opportunity  for  quantitative  research.  The 
efficiency  of  both  flower  and  insect  is  susceptible  of  much  greater  accuracy 
of  measurement  and  it  appears  probable  that  this  will  disclose  a  new  field 
of  correlations.  In  this  connection  the  experimental  study  of  competition 
is  especially  significant  and  promises  to  throw  a  flood  of  light  upon  reciprocal 
adaptation,  as  is  likewise  true  of  mutilation  experiments.  This  leads  to 
the  consideration  of  the  evolution  and  phylogeny  of  flowering  plants  under 
the  influence  of  insect  and  wind  pollination,  as  well  as  a  re-examination 
of  the  effectiveness  of  cross  and  self  pollination.  With  respect  to  the 
insects  the  major  queries  concern  the  respective  roles  of  the  senses,  the 
acquisition  and  fixity  of  habits,  and  the  relation  between  instinct  and 
intelligence. 

METHODS. 

General  principles.— An  endeavor  has  been  made  to  develop  a  compre- 
hensive system  of  research,  based  primarily  upon  experiment  and  measure- 
ment. This  has  been  made  as  complete  as  possible,  though  it  is  fully 
recognized  that  the  further  development  of  this  great  field  will  reveal  new 
objectives  and  new  methods  of  attack.  The  great  majority  of  the  methods 
have  been  tested  in  the  present  study,  others  are  now  being  used  in  the  work 
under  way,  and  a  few  are  still  to  be  applied.  Most  of  the  latter  have  been 
employed  by  other  investigators  and  hence  are  considered  for  the  sake  of 


INTRODUCTION   AND   METHODS.  5 

completeness.  The  observational  method  has  necessarily  been  continued 
in  connection  with  normal  pollination  and  the  life-history  of  the  flower, 
but  it  has  been  made  as  quantitative  as  possible  and  has  frequently  been 
supplemented  by  experiment.  The  experimental  methods  have  been  made 
as  simple  and  direct  as  possible  and  have  been  applied  chiefly  to  attraction, 
behavior  at  the  flower,  and  competition  between  flowers  in  this  first  series. 
Most  of  them  have  been  subjected  to  repeated  check  and  the  results  are 
thought  to  be  fairly  conclusive  for  the  region  and  the  time  concerned. 
The  conditions  have  differed  materially  from  those  obtaining  in  practically 
all  other  studies  in  this  field,  in  that  both  flowers  and  insects  were  in  the 
natural  relations  that  have  existed  for  a  long  period.  While  gardens  yield 
behavior  results  of  as  much  interest  as  those  of  natural  habitats,  it  is  obvious 
that  their  essentially  exotic  nature  renders  them  of  little  value  in  questions 
of  adaptation  and  evolution.  This  difference  is  also  to  be  taken  into  account 
in  other  respects;  for  example,  artificial  flowers  appear  to  be  much  more 
readily  visited  in  gardens  than  in  nature,  as  would  be  expected  from  the 
difference  in  the  habits  of  the  insects. 

Moreover,  it  is  thought  that  the  experimental  investigation  of  a  native 
insect  fauna  in  the  midst  of  its  natural  floral  environment,  and  the  con- 
verse, furnishes  a  norm  to  which  can  be  referred  other  studies  that  are 
artificial  in  some  degree.  Some  such  standard  appears  indispensable, 
since  it  is  evident  that  many  of  the  contradictions  and  discrepancies  in  the 
results  of  various  investigators  are  to  be  explained  by  differences  in  con- 
ditions and  setting  rather  than  by  faults  of  method  or  observation.  This 
is  certainly  true  of  many  of  the  points  at  issue  between  Plateau  and  his 
critics.  The  effects  of  time,  place,  weather,  grouping,  etc.,  are  often 
decisive,  as  shown  in  the  next  chapter,  and  they  need  always  to  be  checked 
by  actual  trial,  or,  much  better,  eliminated  by  simultaneous  observations 
in  contiguous  areas  in  so  far  as  possible.  The  time  of  day,  week,  or  season 
not  only  has  an  effect  due  to  lapsed  time,  but  also  one  especially  of  differ- 
ence in  sun,  cloud,  temperature,  wind,  condition  of  flowers,  habit  of  insects, 
etc.  Even  the  weather  of  the  previous  day  may  have  a  profound  effect, 
if  it  has  been  rainy,  unusually  cold  or  warm,  or  windy.  Differences  of 
location  and  particularly  region  usually  produce  decided  effects,  owing  to 
changes  of  conditions  as  well  as  of  flower  and  insect  populations.  In  fact, 
marked  differences  of  behavior  have  been  noted  in  spots  a  yard  apart 
where  no  differences  of  sunlight,  temperature,  or  wind  were  demonstrable 
at  the  time,  but  where  the  behavior  of  the  insects  had  been  determined  by 
earlier  shade,  exposure,  by  nearness  to  their  nests,  etc.  The  kinds,  number, 
and  grouping  of  the  species  and  individual  flowers  naturally  have  a  pro- 
nounced effect,  as  do  also  the  time  of  blooming,  the  position  in  the  flowering 
period,  the  nectar  flow,  and  the  rate  of  nectar  production.  It  is  equally 
evident  that  the  composition  of  the  insect  fauna  as  to  orders  and  species, 
the  number  of  individuals,  the  sexes,  social  habits,  age,  etc.,  will  greatly 
affect  the  results.  Finally,  it  has  been  found  that  the  position  and  nearness 
of  the  observer,  as  well  as  his  clothing  (cf.  Lovell,  1914:407),  produce 
effects  to  be  taken  into  account,  while  an  increase  in  the  number  of  observers 
in  the  same  spot  may  completely  change  the  response.  Still  other  factors 
enter  into  the  problem,   thus   completing  the  certainty  that  researches 


6  EXPERIMENTAL  POLLINATION. 

widely  removed  in  time  and  space  will  differ  much  in  detail  and  often  in 
principle  as  well. 

Normal  pollination. — This  is  primarily  a  matter  of  observation  and 
is  important  in  experimental  studies  chiefly  because  it  furnishes  a  back- 
ground of  normal  behavior  against  which  departures  may  be  measured. 
The  methods  are  simple  and  have  long  been  exemplified  in  the  works  of 
Delpino,  Hildebrand,  Axell,  Mueller,  Darwin,  Kerner,  Knuth,  Loew, 
MacLeod,  Robertson,  and  others.  For  the  more  exact  results  needed  in 
connection  with  experiments,  it  has  proved  necessary  to  enter  into  finer 
details  as  to  behavior,  to  deal  with  a  larger  number  of  individuals,  and 
especially  to  record  the  number  of  visitors  of  each  species,  as  well  as  the 
number  of  flowers  visited  by  each  individual.  The  failure  to  note  the 
number  of  visitors  of  each  species  deprives  practically  all  of  the  observa- 
tional studies  of  any  quantitative  value,  in  spite  of  the  contention  of  Knuth 
(1906:195)  that  the  "statistical"  method  of  Mueller  has  greater  possi- 
bilities than  one  would  be  inclined  to  believe  and  that  the  reproach  of 
affording  an  inaccurate  idea  of  the  number  of  pollinators  because  it  counts 
the  visits  of  species  and  not  of  individuals  is  of  no  importance.  This  is 
contradicted  by  the  earlier  statement  that  'a  disadvantage  is  involved, 
though  one  that  can  hardly  be  avoided,  as  it  is  almost  impossible  to  count 
all  the  individual  visits  to  a  conspicuous  flower.' 

In  a  critique  of  Knuth's  "Bliitenbiologie,"  Roberston  (1922:148)  states 
that  anthecological  data  "are  lists  of  insect  visitors  made  to  show  the 
species,  their  frequency,  their  efficiency  as  pollinators,  and  the  possibility 
of  their  having  some  influence  in  determining  the  characters  of  the  flowers. 
Mueller's  lists  show  these  details.  In  the  case  of  the  bees  he  indicated 
the  sexes,  and  whether  they  were  sucking  nectar  or  collecting  pollen.  To 
note  the  sexes  is  important,  because  female  bees  fly  longer  than  males  and 
are  more  likely  to  make  repeated  visits.  To  note  the  fact  of  pollen- 
collecting  is  also  important.  A  female  bee  will  carry  pollen  all  day  from 
flowers  on  which  the  male  rarely  occurs.  From  observations  at  Carlinville 
the  females  of  nest-making  bees  average  20.6  visits  to  the  males  10.3.  The 
inquiline  bees  show  females  8.8  to  males  8.0.  In  anthecology  Mueller's 
lists  are  valuable  as  regards  species  and  visits,  but  they  fail  to  indicate  the 
frequency.  In  1908  I  rejected  Mueller's  method  and  adopted  the  practice 
of  capturing  the  individuals  as  they  came,  noting  species  and  counting 
individuals  It  is  impossible  to  indicate  the  importance  of  insects  to  flowers 
by  lists  of  species,  because  efforts  to  increase  the  lists  involve  an  exaggera- 
tion of  the  importance  of  rare  and  exceptional  cases." 

Experimental  pollination. — This  includes  practically  all  the  experi- 
mental methods  that  deal  with  the  relations  of  flowers  and  insects,  though 
competitive  methods  are  considered  separately  for  the  sake  of  convenience. 
No  sharp  line  can  be  drawn  between  these  and  the  methods  that  make  use 
of  colored  objects  or  odorous  substances,  but  it  seems  better  to  consider 
the  latter  in  a  separate  section.  Experiments  may  be  devised  to  show 
the  role  of  different  parts  in  attraction,  landing,  or  guidance,  the  behavior 
of  insects  in  securing  nectar  or  pollen,  or  their  efficiency  in  the  transfer  of 
pollen.     However,  in  many  cases  two  or  more  of  these  processes  are  affected 


INTRODUCTION   AND   METHODS.  7 

by  the  same  change,  and  for  this  reason  the  various  experimental  methods 
are  organized  with  respect  to  the  change  concerned.  There  is  almost  no 
limit  to  the  number  of  changes  and  combinations  that  ingenuity  can  devise, 
but  the  following  discussion  is  restricted  essentially  to  changes  that  have 
been  used  or  are  now  in  process  of  being  used. 

Organization  of  experiments. — All  experiments  have  been  made  in 
the  field  under  natural  conditions.  Controls  have  been  regularly  employed 
and  the  results  checked  by  repetition.  Comparative  values  have  been 
secured  by  using  a  definite  number  of  flowers,  an  equal  area,  or  an  equal 
number  of  them.  The  latter  method  alone  seems  to  be  entirely  without 
error  and  has  completely  replaced  the  others,  since  it  yields  exact  and 
directly  comparable  expressions  of  choice.  For  the  same  reasons  experi- 
ments should  be  observed  at  similar  times  and  for  periods  of  the  same 
length  in  so  far  as  possible.  For  the  best  results  it  is  often  necessary  to 
have  two  or  three  observers,  so  that  the  time  difference  can  be  eliminated 
and  the  same  group  of  competing  insects  followed  under  the  same  condi- 
tions. The  grouping  of  the  plants  and  the  relative  position  of  the  flowers 
are  matters  of  much  importance  and  must  be  considered  with  reference  to 
the  habits  of  the  insects  and  the  type  of  behavior  to  be  tested.  All  experi- 
ments carried  on  with  a  plant  or  group  that  insects  have  been  in  the  habit 
of  visiting  must  reckon  with  the  effect  of  the  habit  itself.  While  such 
results  are  dependable  as  to  behavior,  they  do  not  permit  an  exact  analysis 
of  the  factors  entering  into  it.  On  the  other  hand,  advantage  may  be  taken 
of  habit  to  insure  certainty  in  regard  to  a  response,  as  when  artificial  or 
mutilated  flowers  are  alternated  in  the  cluster  with  normal  ones.  It  must 
also  be  recognized  that  the  reactions  of  mature  insects  contain  a  large 
element  of  habit  and  that  the  real  response  to  certain  stimuli  can  be  obtained 
only  by  using  young  ones  that  have  just  emerged.  Moreover,  it  has  become 
more  and  more  desirable  to  deal  adequately  with  individual  behavior, 
and  this  can  be  done  only  by  working  with  marked  bees. 

Plateau  has  more  than  once  pointed  out  that  experiments  with  flowers 
and  insects  demand  the  greatest  patience  and  almost  unlimited  time,  and 
that  one  must  expect  to  have  many  of  them  rendered  incomplete  by  changes 
of  weather  and  other  hazards.  The  problem  is  the  same  as  in  all  experi- 
mentation in  nature  and  must  be  met  in  so  far  as  possible  in  the  choice  of 
the  region,  the  detailed  organization  of  plans,  and  the  introduction  of  the 
maximum  degree  of  control. 

The  modifications  brought  about  for  experimental  purposes  may  be 
grouped  as  follows:  (1)  changes  of  place,  grouping,  or  time;  (2)  concealing 
or  disguising  flowers  or  clusters;  (3)  removal  or  mutilation  of  flowers, 
parts,  markings,  etc.;  (4)  artificial  or  painted  flowers  or  parts;  (5)  addition 
of  flowers,  parts,  substances,  etc. ;  (6)  combinations  of  two  or  more  changes. 
The  distinctions  between  the  different  types  of  modification  are  far  from 
absolute  and  certain  changes  might  well  be  placed  in  another  group. 

Change  of  position  or  place. — These  may  concern  the  plants  or  flowers 
of  one  species,  or  of  two  or  more  species.  In  the  latter  case  they  have  to 
do  primarily  with  competition  and  are  considered  later  under  that  heading. 
Changes  that  have  to  do  with  the  time  of  blooming  or  the  grouping  may  be 


8  EXPERIMENTAL  POLLINATION. 

utilized  to  hasten  or  retard  flowering  or  to  increase  the  total  attraction  of 
a  group  of  individuals.  Changes  of  position  are  especially  valuable  in 
connection  with  the  study  of  normal  behavior  and  in  determining  the 
correlation  between  habit  and  intelligence  in  different  species  and  indi- 
viduals. They  may  deal  with  the  cluster,  the  flower,  or  the  flower  part, 
but  in  the  last  case  the  change  is  essentially  a  mutilation  and  is  considered 
as  such.  The  simplest  method  is  to  change  the  entire  cluster  in  position 
by  90  or  180  degrees,  either  by  bending  and  fastening  it  in  the  position 
desired,  or  by  cutting  it  off,  placing  the  end  in  a  vial  or  in  wet  cotton,  and 
attaching  it  alongside  a  normal  inflorescence.  The  use  of  single  flowers 
permits  a  wider  range  of  changes,  as  these  can  be  turned  through  two  circles 
with  the  assumption  of  very  different  positions.  Such  changes  not  only 
affect  the  appearance  of  the  flower  with  respect  to  attraction,  but  they 
necessitate  a  different  behavior  in  one  or  more  of  the  successive  processes 
of  landing,  guidance,  obtaining  nectar,  collecting  pollen,  and  departure. 
A  completed  visit  thus  becomes  a  new  problem  in  the  solution  of  which 
species  and  individuals  exhibit  striking  differences. 

Concealing  or  disguising  flowers. — This  may  operate  upon  the  plant 
or  cluster,  a  single  flower,  or  a  part  of  it,  such  as  the  petals  or  stamen-mass. 
When  the  nectary  is  obstructed  by  a  cotton  plug,  the  effect  is  essentially 
one  of  mutilation,  while  the  use  of  green  leaves  to  mask  the  corolla  or 
the  disguising  of  the  rays  of  one  species  with  those  of  another  produces 
an  artificial  flower  in  effect.  Masking  is  primarily  a  device  to  conceal  the 
color  and  thus  permit  the  determination  of  the  role  of  odor,  but  it  must 
always  be  done  with  the  effect  of  habit  in  mind.  Clusters  or  single  flowers 
may  be  covered  with  pots,  boxes,  wire  cages,  or  other  objects,  or  they  may 
be  variously  disguised  by  means  of  paper,  cloth,  leaves,  etc.  The  perianth 
may  be  similarly  covered  on  either  one  or  both  faces,  one  or  more  of  the 
petals  covered,  the  anthers  or  nectaries  masked  with  paper,  cotton,  or 
foreign  petals;  in  short,  any  part  or  parts  may  be  concealed  in  any  manner 
that  seems  desirable.  This  is  similarly  true  of  the  rays  and  disks  of  com- 
posites, and  of  all  vexillary  organs,  such  as  spathes,  colored  bracts,  etc. 
Painting  the  petals  or  other  parts  is  also  a  type  of  masking.  Finally,  odor 
may  also  be  masked  by  means  of  glass  globes,  tubes,  etc.,  permitting  color 
and  form  to  act  alone  as  attractive  factors. 

Mutilation. — By  this  is  understood  the  removal  of  flowers  or  parts, 
the  splitting  or  cutting  of  parts,  and  such  changes  of  position  as  result  in 
a  different  form.  The  removal  of  flowers  is  chiefly  significant  in  such 
definite  inflorescences  as  the  umbel  and  head  with  show-flowers  or  ray- 
flowers,  in  which  all  or  part  of  either  kind  of  flower  may  be  cut  out  to  dis- 
close the  role  of  the  other.  With  respect  to  other  changes  a  radiate  head 
resembles  a  single  flower  to  a  considerable  degree.  In  regular  flowers  the 
most  important  mutilations  arise  from  the  removal  of  corolla  or  perianth 
in  whole  or  in  part,  the  shortening  of  the  petals,  or  splitting  them  into 
parts  of  various  forms.  The  mutilation  of  irregular  flowers  may  also  be  made 
to  throw  light  upon  attraction,  but  it  is  particularly  valuable  in  revealing 
the  role  of  the  specialized  parts,  as  in  the  larkspur,  peas,  and  mints.  Hoods, 
spurs,  standards,  keels,  and  lips  may  be  removed  wholly  or  partly,  or  they 


INTRODUCTION   AND   METHODS.  9 

may  be  variously  split  to  increase  the  attractive  surface.  In  the  interior 
of  the  flower  any  or  all  of  the  stamens,  staminodes,  or  pistils  may  be  removed 
or  modified,  one  or  more  of  the  nectaries  excised  or  otherwise  changed,  and 
the  protective  hairs  of  various  sorts  trimmed  or  cut  as  desired.  All  vexillary 
organs  external  to  the  flower  may  be  treated  in  the  same  manner  as  petals. 
Decisive  changes  in  form  may  be  effected  by  bringing  petals  together  or 
turning  them  back,  or  by  treating  them  to  produce  an  artificial  zygomorphy, 
while  the  internal  arrangement  of  the  flower  may  be  modified  by  changing 
the  position  of  stamens,  staminode,  style,  scales,  etc.  It  is  obvious  that 
the  nectar  may  be  completely  removed  and  the  odor  also  modified  in  various 
ways.  Two  or  more  mutilations  may  be  combined  in  the  same  flower  or 
progressive  mutilation  may  be  carried  out  in  a  series,  ranging  from  normal 
flowers  through  those  with  more  and  more  parts  removed  until  the  pedicel 
alone  is  left.  Finally,  mutilation  may  be  applied  to  the  guide  lines,  stripes, 
grooves,  etc.,  but  these  are  usually  best  modified  by  masking  them  with 
water-colors. 

Artificial  and  painted  flowers. — Between  the  purely  artificial  flower 
at  one  end  of  the  series  and  the  painted  natural  flower  at  the  other  lie  many 
forms,  which  differ  chiefly  in  the  degree  to  which  artificial  or  foreign 
materials  are  used.  Artificial  flowers  proper  may  be  made  of  paper,  cloth, 
wax,  or  other  materials,  and  may  be  either  crude  or  accurate  copies  of 
natural  flowers,  according  to  the  purpose  intended.  Plateau  has  raised 
many  objections  to  those  used  by  his  critics  (p.  163),  but  these  seem  to  have 
little  weight  (p.  239).  Flowers  with  one  or  more  artificial  parts  are  termed 
composites  and  usually  consist  of  the  natural  center  of  a  flower  or  head 
supplied  with  artificial  petals  or  rays.  In  some  cases  the  entire  flower 
or  head  is  used  and  accessory  colored  parts  added.  Artificial  stamens, 
staminodes,  or  pistils  may  be  added  in  special  cases  to  replace  the  natural 
ones,  but  such  uses  are  limited.  Imitations  may  be  made  of  green  leaves, 
with  or  without  natural  centers,  and  they  are  also  fashioned  by  using  the 
centers  or  disks  of  one  species  with  the  petals  or  rays  of  another.  One 
modification  of  particular  value  consists  in  replacing  the  nectaries  or  anthers 
of  one  species  with  those  of  another.  The  best  results  have  been  obtained 
with  natural  flowers  painted  with  water-colors,  since  these  are  artificial 
only  in  color.  Such  paints  may  also  be  employed  to  mask  stripes  and  spots 
or  to  supply  new  markings  to  test  the  directive  value  of  the  guide  lines. 
In  certain  cases  natural  flowers  may  be  killed  by  the  vapors  of  osmic  acid 
or  otherwise,  or  they  may  be  used  in  the  dried  form  when  the  petals  or  rays 
are  papery  in  texture.  Bits  of  colored  paper  or  cloth,  or  detached  petals, 
have  something  of  the  value  of  artificial  flowers,  but  belong  properly  in 
the  category  of  colored  objects  that  can  be  employed  to  test  color  vision. 

Addition  of  parts  or  substances. — Additional  parts,  such  as  petals, 
rays,  stamens,  etc.,  may  be  supplied  from  flowers  of  the  same  species  or 
from  those  of  different  species.  Perhaps  the  most  interesting  change  of 
this  kind  is  where  the  number  of  nectaries  is  doubled,  and  especially  when 
those  of  another  species  are  alternated.  In  flowers  where  the  nectar 
accumulates  in  considerable  amounts  in  tube  or  spur,  it  may  be  withdrawn 
and  exchanged  with  that  of  a  different  species.     Pollen  may  similarly  be 


10  EXPERIMENTAL  POLLINATION. 

transposed  or  the  same  result  obtained  by  the  exchange  of  stamens.  In 
the  great  majority  of  cases,  however,  addition  deals  with  honey  or  sugar 
solutions  on  the  one  hand  or  odorous  substances  on  the  other  in  order  to 
determine  the  role  in  attraction.  The  results  with  odors  depend  largely 
upon  whether  these  are  natural  ones  to  which  the  insects  are  accustomed 
to  respond  and  the  best  method  is  to  employ  fragrant  flowers  or  parts 
regularly  visited. 

Competition. — Competition  is  regarded  as  natural  when  plants  of  two 
or  more  species  grow  so  close  or  intermingled  that  their  flowers  compete  for 
the  same  group  of  visitors.  It  is  brought  about  artificially  when  plants, 
clusters,  or  flowers  are  transferred  in  such  manner  as  to  result  in  com- 
petition. The  distinction  practically  disappears  when  individuals  are 
transplanted  or  seeds  sown  in  such  a  way  as  to  form  a  competition  group. 
Natural  competition  groups  are  also  constituted  when  the  flowering  period 
of  one  species  is  retarded  by  pruning  or  cutting  back,  or  accelerated  in 
various  ways  to  cause  it  to  overlap  in  some  degree  the  period  of  an  associated 
species.  However,  when  one  or  more  species  are  transplanted  to  a  different 
climax  or  region,  the  resulting  group  is  more  or  less  artificial  in  its  relations. 
As  a  rule,  the  simplest  method  is  by  the  transfer  of  inflorescences  or  single 
flowers,  which  are  kept  fresh  in  bottles  of  water  or  by  means  of  wet  cotton. 
Clusters  have  the  advantage  in  saving  time  and  effort  and  in  exerting  a 
stronger  attraction  for  visitors.  The  best  results  are  obtained  when  two 
species  are  employed  reciprocally  as  bouquet  and  plant  at  the  same  time, 
but  this  demands  two  observers.  Mixed  bouquets  of  two  or  more  species 
or  separate  bouquets  of  the  same  often  give  good  results  with  a  single 
observer.  When  visitors  are  not  too  abundant,  as  many  as  a  half-dozen 
species  may  be  followed  at  one  time  if  the  flowers  are  close  together  and  not 
too  numerous.  Most  mutilation  experiments  are  essentially  studies  of 
competition  between  normal  and  mutilated  flowers  and  it  is  often  profitable 
to  combine  these  with  competition  tests  between  normal  flowers  of  several 
species.  It  is  especially  desirable  to  have  the  number  of  flowers  or  heads 
the  same  for  each  competitor,  and  this  is  secured  by  basing  the  number 
in  bouquet  or  cluster  upon  that  in  the  group  to  be  used,  or  by  removing 
flowers  to  the  number  desired.  Since  the  standard  or  species  in  the  natural 
position  is  regularly  favored  in  consequence  of  the  habit  of  the  visitors,  it 
is  desirable  to  scatter  the  competitors  through  the  group,  as  they  may  other- 
wise remain  unnoticed. 

Manipulation  of  insects. — As  has  been  indicated,  it  is  felt  that  the 
greatest  advance  in  the  study  of  insect  behavior  can  now  be  made  by 
dealing  with  individuals.  This  not  only  permits  greater  accuracy  in 
organizing  the  results  for  orders,  genera,  and  species,  but  it  also  opens  up 
a  new  and  fertile  field  scarcely  touched  as  yet.  A  prerequisite  for  such  work 
is  a  simple  and  rapid  method  of  catching  and  marking  individuals,  such 
as  the  one  devised  by  Giltay  (1906:468).  While  this  will  demand  still 
more  time  and  patience,  the  gain  in  detail  and  accuracy  over  present 
methods  will  be  as  great  as  that  secured  by  replacing  lists  of  species  by  a 
record  of  visitors  and  visits.  In  fact,  the  actual  number  of  visitors,  espe- 
cially in  terms  of  flight  from  the  nest  or  hive,  can  be  determined  in  no  other 


INTRODUCTION   AND   METHODS.  11 

way.  Many  new  facts  are  revealed  as  to  flight,  speed  of  working,  constancy, 
seasonal  adjustment  in  relation  to  changing  maxima  of  flowering,  and  so 
forth. 

The  analysis  of  behavior  rests  upon  three  factors — instinct,  habit,  and 
individual  adjustment.  Instinct  is  here  regarded  as  fixed  habit,  and  can 
be  largely  evaluated  by  investigating  the  comparative  behavior  of  related 
species  and  genera.  It  is  probable  that  habit  is  constantly  passing  over 
into  instinct,  as  seems  well  illustrated  by  the  perennial  adjustment  made 
by  groups  of  species  and  individuals  in  the  particular  floral  environment 
to  which  their  round  of  activities  is  restricted.  As  both  observation 
and  experiment  have  shown,  visits  to  flowers  are  largely  determined  by 
habit,  and  it  is  impossible  to  secure  conclusive  evidence  as  to  the  senses 
and  mental  powers  of  insects  without  eliminating  this  actor.  The  best, 
though  hardly  the  simplest,  way  of  doing  this  is  to  base  all  studies  of 
attraction,  for  example,  upon  the  use  of  individuals  that  have  just  hatched 
and  hence  have  had  no  opportunity  to  form  habits.  This  demands  the 
location  and  control  of  nests  and  the  marking  of  individuals  as  they  emerge. 
It  can  be  done  in  a  less  exact  manner  by  transferring  nests  or  hives  to  a 
different  climax,  as  from  the  plains  at  the  foot  of  Pike's  Peak  to  the  montane 
or  alpine  zone,  but  even  here  marking  or  cages  must  be  employed  for 
accurate  results,  except  where  a  species  peculiar  to  the  plains  is  used. 
Pollination  cages  afford  the  best  means  of  complete  control,  but  those  so 
far  employed  have  separated  nest  and  flower  group,  with  the  result  that 
the  caged  bees  finally  became  panic-stricken.  Cages  several  meters  long 
and  high  enough  to  accommodate  an  observer  when  seated,  into  which  nests 
are  introduced  before  the  young  emerge,  furnish  an  almost  ideal  installation 
for  the  study  of  initial  responses  to  color,  form,  and  odor  and  the  gradual 
fixation  of  habits.  These  can  then  be  removed  with  their  occupants  to  a 
totally  different  group  of  species,  or  the  flowers  to  which  they  are  accus- 
tomed can  be  mutilated  to  call  forth  new  responses  and  the  consequent 
adjustment  of  habits  to  new  conditions.  Here,  as  in  all  experimental 
ecology,  the  basic  problem  is  to  secure  laboratory  control  under  field 
conditions,  and  the  pollination  cage  appears  much  the  best  solution. 
However,  there  will  always  remain  certain  experiments  that  can  be  carried 
on  best  or  solely  in  the  laboratory,  where  maximum  control,  uniformity, 
and  accuracy  can  be  secured.  The  requisite  technique  has  been  so 
carefully  developed  by  Frisch  (1914,  1919)  and  Knoll  (1921,  1922)  that 
their  methods  will  serve  as  the  point  of  departure  for  all  such  work  in 
this  field  (cf.  also  Porsch,  1922:485). 

The  most  conclusive  evidence  as  to  the  role  of  color  in  attraction  has 
been  furnished  by  insects  with  the  antennae  coated  or  amputated,  even 
Plateau  admitting  its  cogency.  The  relatively  small  number  of  experi- 
ments made  with  anthophilous  insects  indicate  the  desirability  of  extending 
such  work,  and  the  questions  raised  by  Mclndoo's  researches  render  this 
imperative.  Owing  to  the  injury  usually  caused  by  the  amputation  or 
excision  of  the  antennae  or  other  organs,  the  chief  task  is  to  discover  a 
substance  that  will  coat  them  with  litt'.e  or  no  injury  and  that  can  not  be 
readily  removed.  All  substances  that  contain  alcohol,  turpentine,  essential 
oils,  etc.,  must  be  avoided  and  the  preference  given  to  mixtures  of  paraffin 


12  EXPERIMENTAL  POLLINATION. 

and  vaselin  with  the  lowest  possible  melting-point  and  corresponding 
penetration.  The  individuals  must  be  marked  and  observed  from  day  to 
day,  and  only  those  utilized  which  are  essentially  normal.  The  tests 
should  be  made  under  natural  conditions  with  materials  to  which  the  insect 
has  been  accustomed,  and  should  meet  the  requirement  laid  down  by 
Forel,  namely,  that  the  insect  recognize  a  certain  substance  and  dis- 
tinguish it  from  others  in  a  constant  and  indubitable  manner  when  normal 
and  not  when  mutilated.  The  application  of  such  tests  to  normal  insects, 
those  with  the  antennae  coated  and  those  with  the  olfactory  pores  cov- 
ered, should  be  decisive.  The  results  can  be  rendered  even  more  decisive 
by  covering  the  insects'  eyes  and  contrasting  the  response  of  insects  with 
either  the  antennae  or  the  olfactory  pores  coated  to  fragrant  flowers  that 
are  habitually  visited.  Many  other  modifications  of  insects  are  possible 
and  can  be  developed  as  need  arises,  such  as  removing  the  scopa,  attach- 
ing artificial  ones,  filling  the  corbiculse  with  wax,  etc.  In  connection  with 
determinations  of  efficiency,  constancy,  etc.,  it  is  helpful  to  stain  the 
pollen  of  various  species  with  particular  dyes  and  thus  simplify  reading 
the  pollen  record  of  its  behavior.  One  of  the  most  interesting  series  of 
experiments  contemplated  deals  with  the  reversal  of  the  characteristic 
habits  of  diurnal  and  nocturnal  pollinators. 

Life-history  methods  and  records. — In  the  endeavor  to  determine  the 
exact  relation  of  the  flower  and  its  behavior  to  the  habitat,  simple  methods 
have  been  devised  for  following  and  recording  all  changes  in  minute  detail. 
Quite  apart  from  yielding  a  complete  account  of  the  development  of  the 
flower,  such  records  have  proved  indispensable  in  correlating  floral  changes 
with  physical  factors  and  insect  behavior,  as  well  as  in  connection  with 
competition  and  autogamy.  The  methods  are  essentially  observational, 
though  the  subject  affords  an  increasing  opportunity  for  the  use  of  experi- 
ments in  the  correlation  of  flowers  or  parts.  The  essential  features  are: 
(1)  labeling  flowers  in  the  order  of  development;  (2)  visiting  the  plants 
sufficiently  often  to  obtain  a  detailed  record;  (3)  recording  changes  on  a 
tabular  form  that  permits  ready  checking  against  the  preceding  observation. 
The  usual  plan  has  been  to  mark  two  or  three  adjacent  plants  and  to  follow 
the  development  of  10  flowers  on  each  simultaneously.  This  furnishes  an 
adequate  check  on  individual  behavior,  and  it  is  practically  impossible  to 
follow  a  larger  group  when  a  number  of  species  is  concerned.  When  the 
buds  are  sufficiently  large,  a  label  is  attached  to  each  and  the  flowers 
are  numbered  in  the  order  of  their  appearance.  Ordinary  price-tags  are 
employed  and  the  size  determined  with  respect  to  the  flower.  In  the  case 
of  minute  flowers,  especially  those  of  umbellifers  and  grasses,  the  smallest 
tags  are  too  large  for  individual  flowers,  and  other  devices  must  be  employed. 
Tags  may  be  placed  at  every  third  or  fifth  flower  in  large  umbels  or  at 
corresponding  spikelets  in  panicled  grasses,  but  in  the  smaller  inflorescences 
this  often  produces  great  distortion.  Diagrams  with  the  flowers  numbered 
sometimes  afford  the  best  solution,  while  with  the  smaller  radiate  heads 
of  composites  the  rays  may  be  numbered  in  ink  and  thus  furnish  divisions 
that  enable  one  to  follow  the  disk-flowers  accurately.  In  large  heads  and 
umbels  and  such  spikes  as  those  of  Phleum,  the  inflorescence  is  labeled  and 


INTRODUCTION   AND   METHODS.  13 

threads  are  used  to  mark  divisions  sufficiently  small  to  permit  following 
the  florets  with  accuracy. 

Visits  are  regularly  made  once  each  day,  except  during  the  rapid  develop- 
ment of  the  warmest  days,  when  morning  and  afternoon  visits  are  often 
necessary.  Once  or  twice  during  each  series,  records  are  taken  in  the  early 
morning,  at  noon,  and  in  the  evening  in  order  to  obtain  the  finest  details 
in  the  changes.  Similarly,  one  or  two  visits  at  sunrise  and  sunset  are 
necessary  to  determine  the  times  of  opening  and  closing  of  many  species. 
The  regular  visit  is  made  in  the  morning,  preferably  at  the  same  hour, 
though  this  must  often  be  modified  as  a  result  of  weather  or  by  other  duties. 
The  use  of  two  persons,  one  to  observe  and  the  other  to  record,  effects  a 
great  saving  of  time,  but  when  this  is  impossible,  the  entire  record  should 
be  made  by  the  same  individual.  The  record  sheet  for  each  species  is 
ruled  to  hold  the  entries  for  20  flowers,  extra  sheets  being  employed  when 
all  the  flowers  of  a  head  or  umbel  are  to  be  taken  into  account.  The  same 
form  is  used  for  both  the  field  and  the  final  typewritten  record  and  an 
endeavor  is  made  to  enter  the  observations  so  that  the  field  sheet  can  be 
copied  directly.  This  necessitates  a  fixed  set  of  abbreviations  in  order  to 
save  both  time  and  space.  The  entries  for  each  visit  are  made  beneath 
the  preceding  one,  the  space  being  left  blank  when  no  change  has  occurred, 
as  this  permits  ready  comparison  with  the  last  condition.  The  date  and 
the  hour  are  entered  in  the  first  column  for  each  species,  the  round  of  visits 
always  being  made  in  the  same  order  to  allow  the  same  interval,  especially 
when  two  or  three  visits  are  made  in  one  day.  A  record  is  kept  of  periods 
of  cloudiness  and  rain,  in  addition  to  the  usual  records  of  temperature  and 
humidity.  The  striking  differences  in  the  rate  of  floral  development  in 
sun  and  shade  ecads  of  the  same  species  have  been  the  subject  of  a  special 
study,  in  which  temperature  and  humidity  were  also  determined  under 
the  forest  canopy. 

Life-history  record  of  a  representative  species. — The  detailed  life- 
histories  have  been  recorded  for  about  100  species  of  the  Pike's  Peak  region. 
For  the  majority  of  these  this  was  first  done  in  the  summer  of  1912  and  has 
been  repeated  in  1921  and  1922,  two  simultaneous  sets  of  readings  being 
taken  in  1921  by  different  observers.  Because  of  the  limitations  of  space, 
the  detailed  table  (table  1)  is  given  for  a  single  species  only,  and  this  is 
restricted  to  10  flowers  on  two  different  plants,  taken  from  the  1921  observa- 
tions. The  main  features  of  the  life-history  of  26  species  are  illustrated 
in  plates  2  to  14,  and  the  stages  described  in  the  corresponding  legends. 


14 


EXPERIMENTAL  POLLINATION. 

Table  1. — Aconitum  columbianum. 


Plant  I. 

Plant  II. 

Date. 

1 

2 

3 

4 

1 
5             6 

7 

1 

2 

3 

July  23,    3  p.m.  02 

24,  10  a.m.  0  4 

4  p.m.   0  6 

25,  10  a.m.     op 

4  p.m.      1 

26,10  a.m.      1 

1 

4  p.m.   .  .  . 

27,  11  a.m.      1 

6 

5  p.m.  .  .  . 

28,  5  p.m.  .  . . 

29,  11  a.m.  .  .  . 

30,  11  a.m.  . . . 

4  p.m.      6 
18 

31,  11  a.m.    18 

4 
4  p.m.      4 

8t 

mm    0  2  mm 
mm    0  4  mm 
mm   0  6  mm 
en        open 
as        2  a  s 
ad       2  a  d 
as        3  a  s 
...      3ad 
...      2  as 
ad       2  a  d 
as        las 

...      lad 
4  a  s 
...      4ad 
...    10  a  s 
...    10  ad 
...      8  as 
ad       8  a  d 
as      st  rec 
ad    

0  2  mm 

0  2  mm 

0  2  mm 

0  2  mm 

0  2  mm 

open 

open 

open 

open 
4  a  s 

0  4  mm 
open 

0  4  mm 
0  6  mm 

0  4  mm 
0  6  mm 

0  4  mm 
0  6  mm 

2  as 

2  ad 
10  as 
10  ad 
8  as 
Sad 
4  a  8 
4ad 
12  a  a 
12  ad 
st  rec 
p  falls 

las 
lad 

9  a  s 
9ad 

2  a  s 
2  ad 
8  as 
Sad 
8  a  s 
10  a  d 
st  rec 
p  falls 

8  a  s 

8  a  d 

4  a  s 
4  ad 
4  a  s 
4  ad 
4  a  s 
4ad 
8  as 
Sad 
st  rec 
p  falls 

2  a  s 

open 

4ad 

4  a  s 

4ad 
12  a  s 
12  a  d 
10  a  s 
10  ad 
st  rec 

2  ad 
2  a  s 
2  ad 
4  a  s 
4  a  d 
19  a  s 
19  a  d 
6  a  s 
6  ad 
las 

1  ad 

2  a  s 
2ad 
2  a  s 
c  enl 

open 

open 

4  a  s 
4  a  d 
4  a  s 

2  a  s 

4ad 
10  as 

10  a  d 
4  a  s 
4  ad 
3  a  s 

3  ad 
las 
1  a  d 

4  a  s 
4  a  d 

st  rec 

2  ad 

2  a  s 
2  ad 
2  a  s 
2  ad 
10  a  s 
10  a  d 
6  a  s 

ad      c  enl 

c  enl 

2,  10  a.m.     c  < 

;nl      c  brwn 
...    p  falls 

c  brwn 
p  falls 

3,    6  a.m.   c  b 

c  brwn 

11  a.m.    p  f 

alls    

p  falls 

Gad 
8  a  s 
st  rec 

4  a  s 
4  a  d 

26  a  s 
aborts 

c  brwn 

p  falls 

pfllg 

o  open, 
a  anther. 


st  stigma. 
c  carpels. 


Contractions. 
shedding.  rec  receptive.  brwn  turning  brownish. 


d  shed. 


enl  enlarging. 


fllg  falling. 


2.  NORMAL  AND  EXPERIMENTAL  POLLINATION. 

Treatment. — In  the  following  treatment  the  species  have  been  arranged 
in  general  accordance  with  their  phylogenetic  sequence,  beginning  with 
the  buttercups  and  terminating  with  the  mints.  The  discussion  of  each  is 
divided  into  two  sections,  the  first  dealing  with  normal  pollination,  the 
second  with  experimental  pollination.  The  experiments  are  considered 
under  four  headings:  (1)  change  of  position;  (2)  mutilation;  (3)  artificial 
and  painted  flowers ;  (4)  addition  of  honey  and  odor.  Those  that  deal  with 
competition  and  constancy  are  reserved  for  the  following  chapter.  Refer- 
ences are  given  to  the  European  and  American  observations  on  the  pol- 
lination of  the  same  or  related  species,  accompanied  by  a  brief  abstract 
where  it  seems  warranted.  Each  table  or  group  of  tables  is  summarized 
in  detail  and  a  rSsume'  of  the  general  results  is  given  at  the  end  of  the  chapter. 
These  are  further  discussed  in  connection  with  the  conclusions  of  other 
investigators  in  the  final  resume1  at  the  end  of  the  fourth  chapter. 

ACONITUM  COLUMBIANUM. 
NORMAL  POLLINATION. 
Structure. — The  hood  in  Aconitum  is  formed  of  two  colored  sepals 
united,  the  other  two  sepals  making  a  landing-platform  for  insect  visitors. 
Two  petals  are  modified  into  nectaries,  while  two  form  the  sides  of  the  hood. 
The  sepals  and  petals  are  colored  alike,  increasing  the  amount  of  color  in 
the  flowers  and  making  them  more  easily  seen  and  attractive.  The  sepals 
that  constitute  the  landing-platform  are  smaller  than  the  other  sepals 
and  petals,  but  large  enough  to  support  the  weight  of  the  visitors.  The 
side  petals  arch  above  the  stamens  and  protect  them  to  some  extent  from 
the  rain,  but  do  not  interfere  with  the  access  of  pollinators.  However, 
they  hide  the  stamens  from  view  when  the  flowers  are  seen  from  certain 
positions.  The  nectaries  are  long  and  stalked,  with  a  crested  hood  at 
the  top.  To  secure  nectar,  the  visitors  must  have  a  proboscis  10  mm. 
long  in  order  to  reach  through  the  stalk  to  the  hooded  portion  containing 
the  nectar  (plate  2). 

Behavior. — The  most  frequent  visitors  to  Aconitum  are  Bombus  juxtus 
and  bifarius,  of  which  the  former  is  far  more  frequent,  evidently  because 
this  species  is  more  numerous  in  the  region.  It  is  larger  than  bifarius 
and  covers  more  of  the  flower.  It  lands  on  the  two  lower  sepals,  with  its 
head  toward  the  base  of  the  nectaries,  and  the  hind  legs  curve  around  the 
small  sepals,  while  the  front  pair  grasp  the  side  ones.  The  under  part  of 
the  thorax  rubs  back  and  forth  against  the  anthers  and  stigmas  as  the  bee 
sucks  nectar.  It  pushes  the  proboscis  into  both  nectaries  and  often  stops 
to  brush  the  pollen  from  its  sides  on  to  its  legs,  as  it  leaves  the  flower. 
B.  juxtus  visits  the  flower  for  nectar,  but  in  getting  this,  pollen  is  brushed  from 
its  hairy  thorax  on  the  stigmas,  and  at  the  same  time  pollen  is  dusted  on  the 
bee.  When  sucking  nectar,  the  tip  of  the  abdomen  reaches  to  the  three 
styles.  The  bee  scrapes  pollen  from  its  head  parts  as  it  leaves  the  flower. 
It  usually  goes  from  the  lower  flowers  on  the  raceme  to  the  upper  ones 
and  then  down  again. 

15 


16  NORMAL  AND  EXPERIMENTAL  POLLINATION. 

Bombus  bifarius  lands  on  the  sepal  platform  with  its  head  above  the  group 
of  stamens  and  pointing  toward  the  base  of  the  nectaries.  It  then  moves 
up  to  such  a  position  that  its  thorax  is  above  the  stamens  and  its  head  is 
at  the  base  of  the  nectaries,  the  hind  legs  resting  upon  the  two  front  sepals. 
As  it  sucks  nectar,  its  body  moves  back  and  forth,  thus  rubbing  the  lower 
side  of  the  thorax  and  abdomen  against  the  anthers  and  stigmatic  surfaces. 

None  of  the  North  American  species  of  Aconitum  has  previously  been 
studied  with  respect  to  its  pollination.  In  Europe,  A.  napellus  and 
lycoctonum  have  received  the  most  attention,  and  Kronfeld  has  pointed  out 
that  the  species  of  this  genus  are  almost  exclusively  bumble-bee  flowers, 
the  areal  limits  of  Aconitum  and  Bombus  coinciding  in  a  remarkable  way. 
In  addition  to  Bombus,  Knuth  cites  only  visits  by  Macroglossa  and  Lycaena 
(1908:50);  in  the  Pike's  Peak  region  the  sole  visitors  are  bumble-bees. 

EXPERIMENTS. 

CHANGE  OF  POSITION. 
Horizontal  racemes. — Racemes  were  placed  in  a  horizontal  position 
and  attached  to  the  normal  ones  by  thread.  Since  the  flowers  of  Aconitum 
are  fastened  at  various  points  around  the  stem,  the  tip  of  the  hood  on 
some  pointed  sidewise  and  in  others  it  pointed  up  or  down.  Both  Bombus 
juxtus  and  bifarius  easily  went  into  flowers  with  the  hood  pointing  down- 
ward, using  the  side  petals  instead  of  the  lower  sepals  as  a  landing  plat- 
form. They  then  secured  nectar  without  taking  an  uncomfortable  position. 
B.  juxtus  hovered  over  the  hood  in  flowers  where  it  pointed  sidewise. 
Finally,  it  went  to  the  open  end  where  the  stamens  were  exposed,  pushed 
its  proboscis  about  as  if  exploring,  and  then  found  the  nectary.  The  next 
flower  had  the  tip  of  the  hood  pointing  up,  and  B.  juxtus  landed  at  once 
on  the  side  petals  and  took  nectar  without  any  inconvenience.  In  another 
case  where  the  hood  pointed  sidewise,  the  bee  hovered  over  the  spur  first, 
apparently  trying  to  find  a  place  to  land.  It  then  went  to  the  side  of  the 
flower  and  attempted  to  land,  but  slipped  off  the  edge  of  the  side  petal, 
succeeding  only  on  the  second  attempt.  The  next  flower  was  horizontal 
with  the  hood  directed  upward.  The  bee  hovered  at  the  spur,  went  to 
the  other  end,  and  landed  easily.  It  did  not  learn  by  one  experience  that 
it  could  find  the  nectar  at  this  end  when  the  flower  was  in  the  horizontal 
position.  In  each  case  it  hovered  where  it  would  normally  expect  to  alight, 
before  going  to  the  place  where  landing  was  possible. 

Racemes  inverted. — Racemes  were  cut  off  and  tied  to  the  plant  in 
an  inverted  position  and  a  piece  of  moist  absorbent  cotton  was  placed 
around  the  cut  end  to  prevent  wilting.  Some  individuals  of  both  Bombus 
juxtus  and  bifarius  found  the  nectar  readily,  while  in  other  cases  they  were 
frightened  away  or  gave  up  too  soon.  The  former  passed  over  some  flowers 
without  attempting  to  land,  and  merely  hovered  near  others.  A  few 
individuals  started  to  alight  and  then  flew  away  as  if  bothered  by  the 
change.  Some  bees  landed  at  the  lower  sepals,  which  now  pointed  up  and 
occupied  the  position  usually  taken  by  the  hood,  turned  around,  and 
quickly  walked  into  the  flower  upside  down.  The  next  flower  was  normal 
and  B.  juxtus  went  to  this  as  usual.     The  third  was  inverted  and  the  bee 


^^ 


;.    ~ 


ACONITUM    COLUMBIANUM.  17 

proceeded  exactly  as  in  the  first  inverted  flower,  apparently  noticing  the 
change  of  position  before  landing.  One  B.  bifarius  mastered  the  situation 
readily  and  went  to  five  inverted  flowers  in  succession,  turning  upside 
down  just  after  alighting  at  each  one.  Another  B.  juxtus  landed  three 
times  at  a  group  of  inverted  flowers,  tried  to  push  its  proboscis  into  the 
hood  without  turning  upside  down,  and  in  each  case  failed  to  find  the 
nectary. 

MUTILATION. 
Cotton  plugs. — When  absorbent  cotton  was  placed  in  the  nectary, 
Bombus  juxtus  landed,  pushed  out  its  proboscis  to  find  the  opening,  and  tried 
repeatedly  to  make  a  way  through  the  cotton  into  the  nectary.  At  the 
next  flower  it  hovered  but  did  not  land.  When  the  styles  and  stamens  were 
hidden  by  a  cotton  wad,  B.  bifarius  made  the  same  unsuccessful  effort  to 
find  the  nectary  opening.  Another  individual  jerked  back  as  it  was  about 
to  land,  and  then  quickly  flew  away  to  the  next  flower.  A  third  hovered 
above  the  flower  and  departed  without  landing,  as  did  several  others  of 
both  species. 

Stamens  removed. — Bombus  juxtus  noticed  the  change  as  readily  as 
when  the  flowers  were  covered  with  cotton  wads,  while  B.  bifarius  either 
hovered  above  the  flower  before  alighting,  or  landed  directly  and  flew  away 
at  once  without  projecting  the  ligule  or  trying  to  find  the  nectar. 

Hood  split. — The  hood  was  split  longitudinally  in  some  flowers,  thus 
making  them  more  conspicuous,  as  it  then  exhibited  a  pair  of  wings  ascending 
behind  the  nectaries.  In  some  cases  this  change  had  no  effect  upon  landing, 
as  it  appeared  neither  to  frighten  the  bees  nor  to  attract  them  in  increased 
numbers,  but  in  others  it  greatly  increased  the  attraction.  They  landed 
in  tHe  usual  manner,  but  had  a  very  hard  time  hanging  on  to  the  stamens. 
Because  they  were  unable  to  find  a  suitable  position,  they  often  went  away 
without  getting  nectar. 

Hood  removed. — The  hood  was  removed,  leaving  the  two  nectaries  to 
project  above  the  remaining  flower-parts.  This  made  the  nectaries  con- 
spicuous and  changed  the  general  aspect  of  the  flower  very  much.  The 
effect  on  the  visiting  bees  was  not  uniform.  Bombus  juxtus  sometimes 
hovered  above  the  flowers,  but  did  not  land,  or  stopped  without  pushing 
out  its  ligule.  Some  exposed  the  ligule,  then  noticed  the  change,  and  flew 
away.  Others  were  more  persistent,  for  they  landed,  at  once  found  the 
slit  down  which  the  nectar  runs,  and  emptied  each  of  the  nectaries,  repeating 
this  performance  at  the  next  flower. 

Hood  and  nectaries  removed. — An  individual  of  Bombus  juxtus 
alighted  as  usual,  and  explored  in  all  directions  with  its  tongue,  in  the 
unsuccessful  endeavor  to  find  the  opening.  One  adventurous  individual 
crawled  between  the  side  petals  as  if  expecting  to  find  the  nectary.  When 
it  got  through,  it  turned  around,  crawled  over  the  stamens,  and  flew  away. 

Lower  sepals  removed. — Since  this  is  the  part  of  the  flower  on  which 
Bombus  usually  rests  its  hind  legs,  it  found  difficulty  in  balancing  properly 
while  seeking  the  nectary,  but  finally  succeeded  in  reaching  the  nectar. 


18 


NORMAL  AND  EXPERIMENTAL  POLLINATION. 


Side  petals  removed. — Some  bees  evidently  noticed  the  changed  appear- 
ance brought  about  when  these  were  removed,  and  hovered  above  the  flowers 
without  landing.  However,  most  of  them  seemed  to  observe  no  change,  for 
they  landed  and  sucked  nectar  as  if  the  flowers  were  normal,  and  even  came 
back  a  second  time.  The  second  pair  of  legs  in  these  cases  was  crowded 
closer  to  the  base  of  the  stamens  and  rested  there.  Flowers  with  side 
petals  removed  were  also  placed  in  the  horizontal  position  with  the  hood 
pointing  upward.  One  bifarius  treated  these  flowers  as  it  did  Rosa  and 
tumbled  about  on  the  stamens,  collecting  pollen  and  making  no  effort  to 
get  nectar.  Another  followed  and  did  the  same  thing.  This  was  in  marked 
contrast  to  all  other  observations  on  normal  Aconitum,  in  which  Bombus 
had  never  made  any  effort  to  collect  pollen.  Ordinarily,  the  pollen  was 
collected  accidentally  as  the  body  moved  back  and  forth  across  the  stamens 
in  the  act  of  gathering  nectar. 

Competitive  relations. — The  five  types  of  mutilation  were  represented 
by  5  flowers  each,  and  these  were  arranged  with  25  normal  ones  (plates 
15  and  16).  Table  2  gives  the  results;  mere  inspections  are  indicated 
by  an  i. 

Table  2. — Visits  to  normal  and  mutilated  flowers. 


Date. 

Time. 

Species. 

Normal . 

Side 

petals 

off. 

Nectary 

and  hood 

off. 

Hood 

off. 

Hood 

split. 

Cotton 

over 

stamens. 

July  27 
July  28 

3  to    5 
9  to  11 

Bombus  juxtus. .  .  . 
Bombus  bifarius.  .  . 
Bombus  juxtus.  .  .  . 

5 
35 

o 
0 

2: 16  i 
2:3i 
a:  Hi 

3 
6 
14 

14 

8 

32 

0 
1  i 
li 

Total 

67             9           9:30i         23         54       2i  :95 

The  number  of  visits  to  the  mutilated  flowers  was  nearly  a  half  greater 
than  those  to  the  normal,  due  chiefly  to  the  response  to  the  flowers  with 
the  hood  split.  This  greatly  increased  the  extent  of  the  color  surface  and 
the  attraction  even  to  a  greater  degree,  as  each  flower  received  4  times  as 
many  visits  as  a  normal  one.  Since  those  with  the  hood  off  averaged 
nearly  twice  as  many  visits  as  the  latter,  the  exposure  of  the  nectaries 
evidently  played  a  part  in  the  attraction.  The  other  mutilations  were 
visited  about  the  same  as  the  normal  flowers,  except  where  cotton  was 
present,  this  change  being  noted  even  in  rapid  flight.  Individual  differences 
in  behavior  were  especially  noted  in  the  case  of  the  flowers  with  the  hood  and 
nectaries  removed.  Three  bees  inspected  these  flowers  to  one  that  landed, 
and  of  the  latter  some  flew  away  at  once,  while  others  extended  the  ligule 
several  times  in  the  endeavor  to  find  the  opening  to  the  nectary. 
ARTIFICIAL  AND  PAINTED  FLOWERS. 

Normal  colors. — The  flowers  of  Aconitum  columbianum  are  either 
blue-purple,  or  white.  The  plants  studied  grew  along  brook-banks  and 
were  lighted  by  sunflecks,  which  made  the  purple  flowers  more  conspicuous 
than  the  white  ones,  though  the  two  were  equally  numerous.     The  response 


ACONITUM    COLUMBIANUM. 


19 


of  Bombus  to  the  two  colors  is  shown  by  table  3,  which  records  the  number 
and  order  of  visits,  each  time  given  representing  a  different  bee. 


Table  3. — Visits  to  white  and  purple  flowers. 

Time. 

Speoies. 

Visits. 

llh00m  a.m 

3  W,  G  P. 

3  W. 
G  W. 

4  P. 

2  W,  1  P,  3  W,  14  P, 

3  W,  3  P. 

2  P,  2  P,  2  P. 
2  W,  9  P,  2  W. 

4  W. 

11  10    <i. m.  .  .           

11  12     a.m.  .  ,           

11  27    a.m.  .                

11  30    a.m 

11  40    a.m 

4  P. 

During  the  40  minutes,  9  bees  visited  75  flowers,  of  which  26  were  white 
and  49  purple.  On  another  day,  63  flowers  each  of  purple  and  white  were 
observed  for  half  an  hour.  During  this  period  Bombus  juxtus  visited  64 
purple  and  68  white  flowers,  and  B.  edwardsi  1  purple  and  3  white  ones.  The 
total  number  of  visits  was  65  to  the  purple  and  71  to  the  white. 

Artificial  flowers. — To  obtain  further  evidence  as  to  color  preference, 
other  colors  were  tried.  This  was  done  in  two  ways:  (1)  by  replacing 
the  corollas  and  calyxes  with  crepe-paper  floral  envelopes,  leaving  stamens, 
pistils,  and  nectaries  intact,  or  surrounding  the  natural  corollas  by  crepe- 
paper  disks,  and  (2)  by  painting  the  perianth  with  water-colors.  Artificial 
corollas  and  calyxes  of  crepe-paper  were  made  to  resemble  those  of  the 
natural  flowers  as  nearly  as  possible,  the  effect  being  essentially  lifelike. 
Yellow,  green,  white,  red,  pale  blue,  and  purple  were  the  colors  used.  The 
artificial  corollas  were  not  attached  until  after  the  bees  had  visited  all 
the  flowers  under  observation,  in  order  to  make  sure  that  nectar  was  pres- 
ent and  that  nothing  about  the  flowers  was  objectionable.  In  placing  the 
artificial  flowers  the  following  combinations  were  used: 

(1)  A  colored  crepe  flower  was  paired  with  a  normal  one  at  various  points  on  the  stem. 

(2)  A  raceme  was  left  with  as  many  normal  as  crepe  flowers  of  the  various  colors,  and 

these  were  scattered  in  no  definite  order. 

(3)  Flowers  of  a  single  color  of  crepe-paper,  but  as  numerous  as  the  normal  flowers, 

were  scattered  at  various  points  on  the  stem. 

(4)  One  half  the  raceme  was  left  normal  and  artificial  corollas  of  one  color  of  crepe- 

paper  were  used  on  the  other  half. 

These  experiments  were  tried  on  several  days  during  the  season  for  four 
different  years,  with  essentially  the  same  results.  Bombus  would  fly 
within  2  cm.  of  the  crepe  flowers,  but  would  then  pass  without  landing. 
The  only  two  exceptions  to  the  above  were  the  flowers  with  the  pale-blue 
and  white  perianths.  Bombus  stopped  at  the  white  ones  and  worked  as 
if  noting  no  difference,  while  pale-blue  flowers  were  visited  at  7  different 
times  by  as  many  individuals  of  juxtus.  In  two  cases  after  visiting  the 
flower  and  taking  nectar,  this  species  returned  for  another  visit. 


20 


NORMAL  AND  EXPERIMENTAL  POLLINATION. 


To  render  the  natural  flowers  more  conspicuous,  strips  of  crepe-paper 
were  cut  a  half-inch  wide  lengthwise  of  the  roll.  Fine  wire  was  run  through 
this  strip  along  one  edge,  making  a  ruffled  disk  which  was  placed  around 
the  stamens  and  nectaries.  An  equal  number  of  normal  flowers  and  of 
those  with  red,  green,  white,  yellow,  or  blue  crepe  ruffles  were  used.  The 
flowers  appeared  very  showy  and  the  nectaries  and  stamens  were  con- 
spicuous. Bombus  juxtus  visited  only  normal  flowers  to  a  total  of  29, 
while  bifarius  stopped  at  but  5  normal  ones.  It  hovered  low  over  green, 
white,  and  blue  modifications,  but  did  not  land  on  them. 

Painted  flowers. — In  further  experiments,  flowers  were  treated  with 
water-colors.  The  white  flowers  were  usually  painted,  as  they  took  the 
colors  better  than  the  purple.  The  perianths  were  washed  on  the  outside 
alone.  Ten  natural  flowers  and  5  of  each  color  were  used,  making  a  total 
of  30  colored  ones,  or  3  times  as  many  painted  as  normal  (plate  1). 


Table  4.- 


-Visits  of  Bombus  juxtus  to  painted  fl 


Date. 

Time. 

Normal. 

Red. 

Vermilion. 

Green. 

Yellow. 

Blue. 

Indigo. 

July  27 

10h50m  to  llh45m 

29 

4 

1     11 

6 

4 

8 

10 

July  28 

10  50          11  15 

11 

0 

4 

2 

3 

7 

2 

Do. 

1  00           2  55 

4 

0 

4 

3 

2 

3 

3 

Do. 

2  55           3  55 

13 

2 

7 

9 

6 

4 

8 

July  30 

10  00          11  30 
Total 

9 

0 

0 

0 

0 

5 

0 

66 

6 

26 

20 

15 

27 

23:117 

While  this  species  visited  nearly  twice  as  many  painted  as  normal 
corollas,  the  actual  ratio  was  39 :  66,  indicating  a  distinct  preference  for  the 
natural  flowers.  Among  the  painted  ones,  blue,  vermilion,  and  indigo  were 
sought  most,  green,  and  yellow  less,  and  red  by  far  the  least. 

The  response  to  the  colored  flowers  varied  at  different  times,  but  the 
general  behavior  of  visitors  is  shown  by  the  following  field  calendar,  derived 
from  another  experiment: 


9h22m  Bombus  juxtus  at  a  blue  flower  as  if 
noting  no  difference,  but  passed 
by  flowers  painted  yellow,  red, 
and  green;  bifarius  passed  by  all 
the  painted  flowers,  but  hovered 
as  if  inspecting  them. 

9  35  Bifarius  passed  over  the  painted 
flowers,  but  flew  slowly  as  it 
looked   them   over. 

9  45     Juxtus,  purple,  orange-red. 

9  50  Juxtus  took  nectar,  then  hovered  above 
red  and  then  purple  flowers. 

9  55  Juxtus,  green,  and  then  flew  past  a 
brown  and  a  green  one,  after 
hovering  above  each  for  a  short 
time. 


llh15n 
11  17 
11  20 
11  21 
11  23 
11  24 
11  26 
11  27 
11  35 


11  37 
11  39 


Juxtus,  green. 

Juxtus,  orange-red  for  45  seconds. 

Bifarius,  red,  red. 

Juxtus,  blue,  purple. 

Juxtus,  yellow. 

Juxtus,  blue. 

Juxtus,  blue. 

Juxtus,  blue,  purple. 

Bifarius,   purple,   orange,   red,   purple, 

blue,  purple;  passed  over  brown 

and  yellow. 
Juxtus,  yellow. 
Juxtus,  purple,  blue;  passed  by  yellow, 

red,  and  green. 
Bifarius,   purple,   blue,   green,   purple, 

red,  white. 


During  the  time  of  the  above  observations,  Bombus  visited  normal 
flowers  as  well  as  the  colored  ones  listed.  A  summary  shows  that  the  bees 
visited  flowers  of  all  colors  used  except  brown.     Of  the  32  visits  recorded, 


ACONITUM    COLUMBIANUM.  21 

10  each  were  made  to  blue  and  purple,  4  to  red,  3  each  to  green  and  orange- 
red,  and  2  to  yellow. 

Both  the  inside  and  outside  of  10  perianths  were  painted  with  each  of 
the  following  colors:  red,  blue,  yellow,  green,  purple,  and  10  normal  flowers 
were  used  for  comparison.  The  following  short  record  shows  the  resulting 
behavior,  each  line  indicating  a  different  visitor: 

Bombus  juxtus,  6  normal,  low  over  blue,  and  then  flew  away, 
normal,  low  over  blue,  and  then  flew  away. 
2  normal,  blue,  2  normal,  blue,  normal, 
normal,  blue,  normal,  blue,  normal, 
normal,  normal, 
blue,  normal. 

ADDITION  OF  HONEY  AND  ODOR. 

Honey. — In  order  to  throw  light  on  the  role  of  nectar  in  attraction, 
four  kinds  of  sweets  were  used,  viz.,  honey,  diluted  honey,  diluted  white 
Karo  sirup,  and  beet-sugar  solution.  These  were  put  on  the  side  petals  of 
some  flowers,  on  the  stamens  and  styles  of  others,  and  in  the  nectary  opening 
of  still  others.  In  some  cases,  Bombus  juxtus  went  directly  to  the  nectary 
of  flowers  with  honey  at  the  sides  of  the  petals,  sipped  as  usual,  and  flew  away 
without  discovering  the  honey.  In  other  cases,  it  flew  down  to  these  flowers, 
almost  landed,  and  then  flew  away  as  if  frightened,  perhaps  by  the  unusual 
appearance.  When  the  various  sugar  solutions  were  put  into  the  nectary 
openings,  Bombus  took  nectar  as  usual,  but  stayed  longer  at  each  flower,  owing 
to  the  increased  supply.  When  Karo  sirup  or  sugar  solution  was  put  on  the 
stamens,  B.  juxtus  and  bifarius  did  not  notice  it  in  some  cases,  for  they  went 
past  to  the  nectary  and  then  flew  away.  Other  individuals  of  B.  juxtus 
landed  in  such  a  way  that  the  mouth-parts  accidentally  touched  the  sirup. 
After  taking  sirup  from  such  a  flower  a  bee  flew  to  a  normal  one,  pushed  its 
ligule  around  the  stamens  as  if  looking  for  more  sirup,  then  advanced  to  the 
nectary  opening,  and  obtained  nectar  as  usual.  In  the  next  flower,  where 
the  stamens  were  covered  with  honey,  it  proceeded  to  take  this  supply  and 
fly  away  without  trying  for  nectar. 

The  procedure  of  Bombus  juxtus  was  various  in  the  flowers  where  the  honey 
drop  was  placed  on  the  stamen  group.  One  bee  landed  without  noticing 
the  honey  on  the  anthers,  but  pushed  its  head  into  the  hood  and  took  nectar. 
Another  alighted  in  such  a  way  that  its  head  touched  the  honey.  It 
obtained  honey  in  3  flowers  of  this  type,  without  paying  any  attention  to  the 
nectary.  A  third  did  not  notice  the  honey  drop,  but  secured  nectar  in  the 
usual  manner.  As  it  started  to  fly  away  its  thorax  stuck  to  the  anthers, 
and  it  scraped  the  honey  from  its  front  legs,  without  even  discovering  that 
it  was  sweet  or  edible.  B.  bifarius  went  in  succession  to  6  flowers  with  drops 
of  honey  on  the  anthers;  it  did  not  notice  the  honey,  but  took  nectar  as  usual. 
B.  juxtus  landed  on  the  lower  sepal  of  a  flower  in  such  a  way  that  its  head 
touched  the  honey  on  the  anthers,  and  it  sipped  until  the  drop  was  all  gone. 
Instead  of  pushing  its  ligule  into  the  nectary,  it  flew  to  the  next  flower, 
where  a  drop  of  honey  was  in  the  same  position,  and  proceeded  to  suck  all 
of  it.  When  it  started  to  fly  away,  its  tongue  stuck  in  the  honey  and  it  had 
a  difficult  time  to  free  itself. 


22  NORMAL  AND  EXPERIMENTAL  POLLINATION. 

Perfumes. — Sachet  powders  and  perfumes  of  various  sorts  were  also 
tried,  but  without  positive  results.  Bombus  juxtus  and  B.  bifarius  hovered 
above  the  flowers  without  landing  in  many  cases,  and  in  others  flew  about 
as  if  not  noticing  them  at  all.  In  one  case  juxtus  alighted  at  a  flower  with 
arbutus  sachet  and  took  nectar  as  if  noting  no  change.  In  general,  if 
Bombus  noticed  the  odor  at  all,  it  seemed  repelled  rather  than  attracted  by  it. 

SUMMARY. 

In  general,  the  bumble-bees  had  less  trouble  with  horizontal  than  with 
inverted  racemes,  though  there  were  marked  individual  differences.  Some 
bees  passed  readily  from  normal  to  inverted  flowers,  adjusting  their  behavior 
to  each  without  apparent  difficulty.  The  use  of  cotton  usually  prevented 
landing,  and  this  was  frequently  the  case  also  when  the  stamens  were 
removed.  In  spite  of  individual  departures  the  other  mutilated  flowers 
were  usually  visited  about  as  much  as  normal  ones.  In  the  competition 
study,  however,  those  with  the  hood  split  or  removed  received  many  more 
visits,  while  those  with  the  hood  and  nectaries  gone  received  3  inspections  to 
one  visit,  and  those  with  cotton  over  the  stamens  obtained  but  rare  inspec- 
tions. 

No  distinction  was  made  between  white  and  purple  in  the  normal  flowers, 
but  blue  and  purple  were  given  a  decided  preference  over  the  other  colors  in 
the  case  of  artificial  and  painted  ones.  Since  white-crepe  corollas  with 
natural  centers  were  visited  normally,  the  choice  appears  to  have  been 
determined  largely  by  the  colors  regularly  present  in  the  species.  With 
the  exception  of  white  and  blue,  none  of  the  artificial  flowers  yielded  visits, 
though  some  of  these  were  inspected.  Painted  flowers,  on  the  other  hand, 
received  a  third  to  a  half  as  many  visits  as  normal  ones.  The  addition  of 
honey  did  not  render  the  flowers  more  attractive,  and  no  positive  results 
were  obtained  with  perfumes. 

DELPHINIUM  SCOPULORUM. 
NORMAL  POLLINATION. 

Habit  and  structure. — The  anthers  are  very  conspicuous  in  young 
Delphinium  flowers.  They  become  erect  when  mature,  taking  a  position 
very  near  the  opening  into  the  nectary  and  after  dehiscence  they  bend  down 
again.  The  two  petals,  which  have  the  tips  deflexed,  then  close  together 
over  the  shrunken  anthers.  As  the  stigmatic  surfaces  mature,  the  styles 
bend  up,  bringing  the  stigmas  near  the  opening  of  the  nectary  (plate  2). 

Behavior. — Bombus  edwardsi  and  juxtus  are  the  most  frequent  visitors 
to  Delphinium.  When  both  species  are  present,  edwardsi  visits  many  more 
flowers  than  juxtus.  The  latter  uses  the  two  lower  sepals  for  a  landing- 
platform,  the  forelegs  resting  on  the  front  spur  of  the  petals  or  on  the  sides 
of  the  sepals.  After  landing,  it  moves  the  head  forward  above  the  stamens, 
pushes  the  ligule  down  the  spur,  and  takes  nectar.  While  it  comes  for 
nectar  alone,  at  the  same  time  pollen  collects  on  the  legs  and  thorax.  The 
flow  of  nectar  in  these  flowers  must  be  rapid,  as  one  individual  went  twice 
to  15  flowers  on  the  same  plant  and  to  9  flowers  three  times  in  succession 
while  on  one  trip,  and  another  individual  visited  22  flowers   twice  on  the 


DELPHINIUM  SCOPULORUM.  23 

same  trip.  B.  juxtus  sometimes  visits  withered  flowers,  stopping  to  seek 
nectar  at  those  in  which  the  lower  side  petals  have  dropped  off.  B.  edwardsi 
and  morrisoni  land  and  take  nectar  in  the  same  manner  as  juxtus.  As 
Thanaos  martialis  lands  on  the  lower  sepals,  the  delicate  ligule  is  pushed 
into  the  nectary  and  the  hairs  on  the  under  side  of  the  head  come  in  contact 
with  the  anthers. 

Robertson  (1889:120)  states  that  the  white  upper  petals  are  a  sure  guide 
to  the  nectar  in  Delphinium  tricorne,  in  which  the  lateral  petals  serve  to 
protect  the  pollen.  It  agrees  with  D.  datum  and  D.  consolida  in  being 
protogynous  and  especially  adapted  to  bumble-bees.  In  Europe  these 
species  are  exclusive  bumble-bee  flowers  (Knuth,  1908:44),  but  Robertson 
notes  several  other  genera  of  bees  and  a  number  of  butterflies  and  moths. 

EXPERIMENTS. 

CHANGE  OF  POSITION. 

Inverted  racemes. — Bombus  juxtus  hovered  above  6  flowers  which 
were  inverted,  but  apparently  noticed  that  something  was  wrong  and 
did  not  land.  At  the  seventh  flower  it  made  an  attempt  at  landing,  but 
found  the  pointed  front  part  of  the  spur  too  narrow.  After  slipping  off 
twice  when  it  tried  to  put  its  hindlegs  in  this  spur,  it  flew  away.  Other 
individuals  flew  above  these  flowers,  but  did  not  alight. 

Horizontal  racemes. — In  these  flowers  the  hood  pointed  down  and 
Bo?nbus  juxtus  was  not  bothered  by  the  change.  It  landed  and  found  the 
nectar  easily,  using  a  side  sepal  and  one  of  the  lower  ones  for  a  landing 
platform. 

MUTILATION. 

Cotton  plugs. — Absorbent  cotton  was  placed  in  the  opening  to  the  spur, 
which  serves  for  the  nectary.  Bombus  juxtus  stopped,  but  when  it  found 
no  opening  did  not  attempt  to  probe  around  the  cotton,  but  went  to  the 
next  flower.  A  slender  cotton  roll  was  placed  in  the  nectary  in  such  a  way 
that  it  projected  1  cm.  in  front  of  the  flower  and  changed  the  whole  aspect 
of  the  latter.  This  bee  landed  on  the  cotton  projection  and  tried  to  find 
the  opening  to  the  nectary,  but  failed.  It  repeated  the  performance  on 
the  next  flower  with  the  same  results. 

Petals  removed. — The  petals,  which  recurve  and  protect  the  stamens, 
were  removed,  thus  making  the  black  group  of  anthers  very  conspicuous. 
The  curved  white  filaments  showed  above  the  anthers,  and  the  nectary 
openings  were  visible  above  the  filaments,  thus  changing  the  aspect  of  the 
flower  materially.  On  the  first  day  of  this  experiment,  Bombus  juxtus 
took  no  notice  of  the  change  and  found  the  nectary  without  difficulty. 
On  another  day  the  results  were  quite  the  reverse  and  5  individuals  passed 
by  these  flowers  during  a  period  of  15  minutes.  B.  edwardsi  went  to  7  of 
the  mutilated  flowers,  apparently  without  noticing  the  difference  (plate  16). 

Spur  removed. — Bombus  juxtus  pushed  its  tongue  back  and  forth  9 
times  in  one  of  these  flowers,  the  tongue  projecting  6  to  7  mm.  beyond  the 
cut  end.  In  another  instance,  the  tongue  was  rapidly  pushed  back  and 
forth  4  times  through  the  opening.  A  third  individual  noticed  the  change 
in  the  flowers  and  did  not  land. 


24 


NORMAL  AND  EXPERIMENTAL  POLLINATION. 


Landing-platform  removed. — The  landing-platform  in  this  flower 
consists  of  the  lower  two  sepals.  When  these  were  removed,  juxtus  hovered 
above  two  flowers  without  landing.  At  the  third  flower  it  landed  success- 
fully by  placing  the  hind  pair  of  legs  on  the  sepals  of  an  adjoining  flower. 

A  comparison  was  made  between  25  normal  and  25  mutilated  flowers, 
consisting  of  5  of  each  type.  In  the  fifth  type  of  mutilation,  pieces  of  grass 
culms  2  cm.  long  were  used  to  close  the  nectary  openings  and  to  change  the 
appearance  of  the  flowers  (table  5). 

Table  5. — Visitors  to  normal  and  mutilated  flowers. 


Species. 

Normal. 

Lower 

sepals 

off. 

Side 

sepals 

off. 

Upper 
petal  and 
spur  off. 

Spur 
off. 

Grass  culm 
in  nectary 
opening. 

Total. 

Bombus  edwardsi 

juxtus 

Total 

14 
15 

7 
1 

7 
2 

6 
2 

9 
1 

2 
2 

31 

8 

29 

8 

9 

8 

10 

4 

39 

The  mutilated  flowers  were  visited  somewhat  more  frequently  than  the 
normal  ones,  the  kind  of  mutilation  making  little  difference,  except  when 
the  grass  section  was  present.  However,  the  two  species  exhibited  a  marked 
difference  in  behavior,  Bombus  edwardsi  visiting  twice  as  many  mutilated 
flowers  as  normal  ones  and  juxtus  but  half  as  many.  In  the  case  of  the 
grass  section,  two  individuals  of  each  species  of  Bombus  tried  hard  to  push 
the  ligule  into  the  nectary,  but  did  not  succeed,  their  persistent  efforts  at 
the  proper  spot  indicating  that  they  knew  where  the  nectary  was. 

ARTIFICIAL  AND  PAINTED  FLOWERS. 
Crepe-paper  corollas. — In  order  to  give  Delphinium  the  same  general 
form  as  Rubus  deliciosus,  disk-like  corollas  of  red,  white,  green,  yellow, 
or  blue  paper  were  placed  around  the  pedicels  after  the  floral  envelopes 
had  been  removed.  This  did  not  change  the  odor  or  the  essential  parts  of 
the  flower,  but  increased  the  size  in  addition  to  changing  the  color.  There 
were  147  open  flowers  under  observation,  10  of  each  of  the  5  colors,  and  97 
normal  ones,  approximately  twice  as  many  normal  as  changed  flowers. 
During  the  hour  and  a  half  of  observation,  Bombus  juxtus  was  the  only 
visitor,  going  to  93  normal  flowers  and  to  one  with  a  green  paper  corolla. 
During  this  time  it  visited  4  normal  flowers  on  one  branch  where  the  majority 
were  blue,  and  5  normal  ones  on  a  branch  where  most  of  them  were  white, 
but  in  neither  case  did  it  venture  to  try  the  artificial  flowers. 

Crepe-paper  corollas  with  spurs. — In  order  to  study  the  response  to 
color  without  change  of  form,  life-like  crepe  corollas  with  spurs  were  used 
to  replace  the  floral  envelopes.  In  addition  to  27  normal  flowers,  4  of  each 
of  the  five  colors,  red,  blue,  green,  yellow,  and  white,  were  used  for  com- 
parison, with  the  following  results.  Three  individuals  of  Bombus  juxtus 
visited  3,  2,  and  3  normal  flowers  respectively,  not  even  stopping  to  inves- 
tigate those  with  crepe  corollas.  Two  B.  proximus  visited  2  normal  flowers 
each  and  no  crepe  ones.     This  group  of  flowers  was  covered  over  night  with 


DELPHINIUM  SCOPULORUM.  25 

a  paper  sack  to  protect  the  crepe-paper  from  the  rain,  this  also  preventing 
'bees  from  securing  the  nectar  until  the  time  of  observation.  B.  juxtus  was 
the  only  visitor  and  the  several  individuals  went  to  9,  3,  2,  3,  5  normal 
flowers  respectively,  some  flying  low  over  the  colored  ones  as  if  inspecting 
them,  but  not  alighting. 

Painted  flowers. — A  further  study  of  the  reaction  of  pollinators  to 
color  was  made  by  means  of  water-colors  (plate  1).  Three  colors,  green, 
red,  and  yellow,  were  represented  by  1 1  flowers  each,  and  these  were  arranged 
so  that  each  one  adjoined  a  normal  flower.  The  first  visitor  was  Bombus 
juxtus,  which  went  to  all  the  green  flowers  once  and  to  some  twice,  but 
visited  no  others.  B.  proximus  visited  3  normal  flowers  in  one  group,  4 
flowers  in  a  nearby  cluster,  and  then  2  green  flowers.  The  last  visitor 
was  a  very  persistent  individual  of  juxtus,  which  came  to  the  flowers  in 
the  following  succession:  10  normal,  3  yellow,  2  green,  1  green,  3  green, 
25  normal,  21  normal,  3  normal,  3  normal,  2  green,  4  normal,  4  green,  4 
yellow.  In  the  next  experiment,  12  normal  flowers  and  6  each  of  red, 
yellow,  green,  and  brown,  were  used,  but  without  being  arranged  in  any 
definite  order.  Three  visitors  came  during  the  hour  of  observation  with 
the  following  results:  2  individuals  of  juxtus  visited  17  and  19  normal  flowers 
respectively  and  edwardsi  3  normal  ones,  none  paying  attention  to  the  colored 
flowers.  Five  days  later,  when  the  same  number  of  colored  and  normal 
flowers  were  used  in  the  same  type  of  arrangement,  the  results  were  quite 
different.  The  first  visitor  stopped  at  a  normal  flower  only,  but  the  next 
one  visited  the  flowers  as  follows:  normal,  green,  blue,  and  normal,  while 
edwardsi  visited  2  normal  flowers  alone.  The  last  juxtus  went  to  normal, 
blue,  yellow,  normal,  normal,  red,  blue,  red,  and  blue  flowers  in  order. 
In  the  next  experiment  5  flowers  each  were  painted  red,  green,  blue,  yellow, 
or  purple,  on  both  sides  of  the  corolla,  and  25  normal  flowers  were  left  on 
the  same  stalk  for  comparison.  B.  edwardsi  visited  127  normal  and  3  blue 
flowers,  but  no  red,  yellow,  purple,  or  green  ones,  flying  low  enough  over  all 
those  painted  to  distinguish  the  colors.  B.  juxtus  visited  116  normal,  4 
blue,  2  green,  and  1  yellow,  but  no  red  flowers. 

The  total  number  of  visits  to  painted  flowers  was  51,  in  contrast  to  323 
to  normal  ones,  the  ratio  being  1 : 7.  The  individual  range  in  behavior  was 
of  the  greatest,  one  juxtus  visiting  green  flowers  alone  and  another  none  but 
normal  ones,  while  a  third  did  not  discriminate  between  them  and  a  fourth 
went  to  twice  as  many  painted  as  natural  flowers.  When  the  colors  em- 
ployed were  red,  yellow,  and  green,  the  latter  was  given  a  marked  preference, 
but  when  blue  was  added,  this  was  visited  more  than  all  others  combined. 

ADDITION  OF  ODOR. 

Perfume. — Rose  perfume  on  absorbent  cotton  was  wrapped  around  the 
pedicels  under  the  flowers  on  one-half  of  the  stalk.  The  flowers  perfumed 
were  on  the  side  away  from  the  wind,  in  order  to  make  the  odor  more  notice- 
able on  the  one  half.  Bombus  juxtus  visited  9  normal  and  2  perfumed 
flowers,  these  being  the  only  visits  during  2  hours  of  observation.  On 
another  day,  carnation  perfume  was  placed  on  cotton  wads  wrapped  around 
the  pedicels  of  one-half  of  the  stalk.  Nearby,  powder  made  from  camphor 
balls  was  sprinkled  at  the  center  of  the  stamens  on  flowers  in  a  similar 


26  NORMAL  AND  EXPERIMENTAL  POLLINATION. 

arrangement.  The  two  odors  were  on  stalks  near  enough  together  for  obser- 
vation, but  not  so  close  that  the  odors  were  likely  to  mingle.  B.  juxtus 
visited  30  normal  flowers  and  29  with  the  carnation  odor  on  one  plant  and 
15  normal  and  20  with  camphor  odor  on  the  other.     B.  proximus  went  to 

27  normal  and  14  with  carnation  odor,  but  none  with  camphor  odor.  Thanaos 
martiales  visited  1  normal  on  the  carnation  stalk,  but  none  with  the  car- 
nation odor,  and  1  normal  and  3  with  the  camphor  odor  on  the  other  stalk. 

B.  juxtus  and  proximus  both  went  from  normal  to  flowers  with  carnation 
odor  and  from  those  to  normal  flowers.  All  told,  83  visits  were  made  to 
normal  and  68  to  perfumed  flowers,  the  number  to  carnation  being  twice 
that  to  camphor. 

SUMMARY. 

The  experiments  with  flowers  in  changed  positions  indicate  that  the 
bumble-bee  not  only  perceives  such  changes  readily,  but  also  distinguishes 
between  the  two  positions  with  respect  to  the  ease  of  landing.  In  general, 
mutilated  flowers  were  visited  as  readily  as  normal  ones,  even  the  removal 
of  the  landing-platform  causing  but  temporary  difficulty.  Individuality  of 
behavior  was  more  or  less  marked  as  usual,  the  removal  of  the  petals  having 
no  effect  on  one  day  and  leading  to  such  flowers  being  completely  ignored  on 
another.  As  a  rule,  the  bees  were  quick  to  learn  the  significance  of  the 
different  changes,  solving  the  problem  of  landing  after  a  few  attempts. 
The  response  to  paper  flowers  with  natural  centers  was  in  sharp  contrast  to 
that  to  painted  flowers;  the  former  received  but  one  visit  to  125  for  normal 
flowers,  while  the  latter  yielded  one  to  each  7  for  the  normal.  This  suggests 
that  the  eyes  of  the  bumble-bee  are  even  more  accurate  than  our  own  in 
perceiving  small  differences  of  color  and  form.  The  figures  in  the  case  of 
visits  to  perfumed  flowers  are  not  decisive,  though  they  indicate  that  the 
bees  found  the  added  odor  somewhat  disturbing. 

The  experimental  results  with  Aconitum  and  Delphinium  are  essentially 
in  harmony,  as  might  be  expected  from  the  ecological  similarity  of  the 
flowers.  Changes  in  position  and  form  produced  much  the  same  response, 
as  did  paper  flowers  and  added  perfume.  In  the  case  of  painted  flowers  of 
Aconitum,  however,  there  were  more  than  half  as  many  visits  as  to  the  normal 
ones,  the  ratio  being  1:1.7  in  contrast  to  1 :7  for  Delphinium. 

RUBUS  DELICIOSUS. 
NORMAL  POLLINATION. 

Habit  and  structure. — The  bushes  of  this  species  are  tall  and  spreading, 
the  branches  profusely  laden  with  flowers  which  are  the  showiest  in  bloom 
during  its  period.  With  respect  to  attraction  the  flower  consists  essentially 
of  a  mass  of  yellow  stamens  surrounded  by  very  large  white  petals,  and 
possesses  a  pleasant  odor.  The  corolla  is  widely  expanded  and  the  stamens 
fully  exposed.  The  nectar  is  formed  at  the  base  of  the  stamens,  where  it 
appears  as  a  circle  of  tiny  drops. 

Behavior. — Bombus  juxtus  collects  pollen  chiefly  with  the  hind  legs 
as  it  tramples  about,  packing  it  in  large  masses  on  them,  the  hairs  of  the 
body  becoming  well  dusted  in  the  process.     As  it  moves  about,  pollen  is 


RUBUS   DELICIOSUS. 


27 


transferred  to  the  stigmas  from  the  under  parts,  or  autogamy  results  as 
the  stamens  are  spread  and  brought  in  contact  with  the  stigmas.  This 
bee  drives  Halictus  out  of  the  flowers  and  occasionally  enters  a  flower 
with  dried  anthers.  Apis  mellifica  walks  around  the  margin  of  the  flower, 
apparently  because  the  anthers  mature  there  first,  and  then  across  the 
center,  ignoring  those  with  brown  stamens.  While  it  is  trampling  about 
and  collecting  pollen,  the  ligule  is  sipping  the  nectar  found  around  the  edge 
of  the  petals  at  the  base  of  the  stamens.  Monumetha  albifrons  works  around 
the  margin  in  similar  fashion,  collecting  pollen  in  smaller  amounts  on  the 
under  side  of  the  abdomen,  legs,  and  head.  Andrena  crataegi  pushes  its 
head  under  the  anthers,  bites  them  open,  and  shakes  the  pollen  out  in 
order  to  pack  it  on  the  hind  legs.  Vespa  germanica  sucks  ■  nectar  in 
various  positions,  often  entering  flowers  in  which  the  anthers  are  quite  dry. 

Variation  in  visits. — In  order  to  determine  the  effect  of  time  and  place 
on  visits,  detailed  calendars  were  made  on  several  different  days  and  in 
several  places.  Since  these  are  too  long  to  be  given,  the  results  are  sum- 
marized in  tables  6  to  9.  In  the  first  series  the  time  alone  was  varied 
by  making  use  of  three  different  days  close  together,  while  in  the  second 
the  two  days  were  taken  at  different  parts  of  the  flowering  period. 

An  hour  and  a  half  of  observation  at  the  Alpine  Laboratory  on  June  10, 
11,  and  13  yielded  the  list  of  visitors  to  100  flowers  (table  6),  the  second 
figure,  as  usual,  indicating  the  number  of  flowers  visited. 


Table  6. — Visitors  on  different  days  in  early  season. 


Species. 


Apis  mellifica 22:127 

Andrena  crataegi 0:0 

sp 0:0 

Bombus  morrisoni 1:1 

juxtus 0:0 

Bombyliad 0:0 

Halictus  pulzenus 0:0 

Monumetha  albifrons. ...  1:1 


June 


5:5 
2:2 
0:0 
1:1 


June 


0:0 
1:1 
2:2 
0:0 
4:4 
0:0 
0:0  10:10 
0:0  I  0:0 


Musca  sp 

Osmia  melanotricha. 

densa 

bruneri 

Papilio  turnus 

Prosopis  elliptica. .  .  . 
Syrphus  americanus. 


Total 29:134 


June 
10 


1:1 

0:0 
2:2 
1:1 
0:0 
0:0 
1:1 


June 
11 


0:0 
0:0 
0:0 
0:0 
0:0 
0:0 


June 
13 


8:8 
1:1 
0:0 

0:0 
2:2 
1:1 

0:0 


23:23.29:29 


Table  7- 

-Visitors  in  mid  and  late  season. 

Species. 

June  23. 

July  6. 

Species. 

June  23. 

July  6. 

62 
10 

7 

4 
7 
0 
6 
3 
2 
0 

1 
0 
0 

0 
8 
5 
0 
0 
29 
7 

Eristalis  arbustorum  .  .  . 

Musca  domestica 

Diptera  (other) 

0 
1 
8 
0 
0 
1 
0 

1 

0 

1 
0 
0 
1 
4 
3 
1 
0 
1 

Halictus  (Evylaeus)  sp. 

pulzenus 

(Lasioglossum) 

Prosopis  basalis 

elliptica 

wootoni 

Andrena  crataegi 

madronitens. . . 

vicina 

Sphex  vulgaris 

Bombua  juxtus 

occidentalis. . .  . 

Pseudomasaris  vespoides 
Total 

112 

61 

28 


NORMAL  AND  EXPERIMENTAL  POLLINATION. 


The  most  significant  variation  was  that  of  Apis,  indicating  the  possible 
fluctuations  from  day  to  day,  but  similar  differences  of  less  degree  are  to 
be  noted  for  practically  every  species. 

The  visitors  noted  at  the  same  time  of  day,  8h30m  to  9h30m  a.m.,  at  the 
same  location,  with  65  open  flowers  in  bloom  and  under  observation  in 
each  case,  are  shown  in  table  7.  The  first  list  represents  the  visitors  at 
about  the  middle  of  the  flowering  season  and  the  second  those  at  the  end. 
There  were  no  plants  of  Rubus  deliciosus  in  bloom  lower  down  in  the  canyon 
at  the  time  the  second  list  of  visitors  was  made. 

Apis  and  Halictus,  the  two  most  important  pollinators  of  the  middle  of 
the  flowering  period,  were  almost  completely  absent  at  the  end,  but  the 
situation  was  exactly  reversed  for  Bombus  and  Prosopis.  On  the  contrary, 
Andrena  maintained  its  number  throughout,  though  the  three  species  showed 
as  many  types  of  distribution. 

Table  8. — Visitors  to  adjacent  areas  on  different  days. 


Species. 

June  5. 

June  7.                    Species. 

June  5. 

June  7. 

12 
35 

37 
4 

10 
1 
1 
0 

14 
4 
4 
4 
2 

1 
5 
5 
1 
1 
2 
1 
2 
0 
0 

0 
1 

2 
0 
1 
0 
0 
0 

1 

3 

Bombus  occidentalis. . .  . 
juxtus  (worker) 
juxtus (queen) . 

bif  arius 

edwardsi 

2             Osmia  bruneri 

0  phaceliae 

1  melanotricha. .  .  . 
0            Pseudomasaris  vespoides 

morrisoni 

Andrena  canadensis.  .  . . 
madronitens.  . 

crataegi 

prunorum.  .  .  . 
vicina 

2             Syrphus  americanus .... 
0            Systoechus  vulgaris .... 

0  Coleoptera 

3 

1  Total 

146 

94 

0 

Table  9. — Summary  by  genera 

Station  1. 

Station  2. 

Genus. 

Species. 

Visitors. 

Species. 

Visitors. 

1 
6 
5 
6 

12 
88 
15 
12 

1 
3 
3 
4 

77 
5 
4 
4 

Reciprocal  checks  at  the  two  stations  showed  that  the  differences  recorded 
were  due  to  location  and  not  to  time.  Since  they  were  situated  in  the  same 
canyon  and  but  150  meters  apart,  it  is  probable  that  the  contrast  between 
the  numbers  for  Apis  and  those  for  Bombus,  Andrena,  and  Osmia  is  to  be 
ascribed  to  the  difference  in  the  associates  of  Rubus  in  the  two  places. 
In  station  1  it  was  grouped  with  Prunus  demissa  and  P.  pennsylvanica, 
while  at  station  2  it  was  associated  with  Geranium  especially.  However, 
it  is  quite  possible  that  the  difference  was  due  to  habit  rather  than  to  any 
difference  in  conditions. 


RUBUS   DELICIOSUS. 


29 


EXPERIMENTS. 

MUTILATION. 

Petals  split  or  shortened. — When  each  petal  was  cut  lengthwise  into 
four  ribbons,  giving  a  daisy-like  appearance  to  the  flowers,  Bombus  juxtus, 
B.  morrisoni,  and  Andrena  vicina  visited  them  just  as  they  did  normal 
flowers.  In  order  to  reduce  the  attractive  surface,  the  petals  were  clipped 
to  half  their  length,  giving  the  corolla  a  rotate  form,  with  no  spaces  between 
the  petals.  The  flowers  used  were  at  the  same  stage  of  development,  the 
number  of  normal  and  mutilated  ones  being  the  same  on  each  day.  Table 
10  shows  the  effect  of  this  reduction  in  attractive  surface. 

Table  10. — Visits  to  normal  and  mutilated  flowers. 


Species. 

June  26. 

June  27. 

Normal. 

Corolla  reduced. 

Normal. 

Corolla  reduced. 

Visited. 

Inspected. 

Visited. 

Inspected. 

60 

22 
0 
2 

11 
1 
3 
1 
2 
2 
1 
0 
0 
1 
1 

13 
9 
3 
2 

13 

15 
5 
0 
1 
1 
1 
0 
1 
2 
0 
0 
0 
3 
2 
0 
4 
4 
1 
1 
3 

5 
5 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 

25 
8 
7 
0 
0 
0 
0 
0 
0 
0 
4 
3 
0 

0 
3 

7 
0 
0 
0 

3 
1 

2 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
2 
4 
0 
1 
0 

2 
1 
1 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 

Andrena  crataegi 

Halictus  pulzenus , 

(Lasioglossum)  sp  .  . . 
Megachile  wootoni 

Prosopis  basalis 

Systoechus  vulgaris 

Pseudomasaris  vespoides 

Eristalis  arbustorum.  .  . 

Muscidae 

Anthrax  lateralis 

Diptera  (other) 

Total 

147 

44 

10 

58 

13 

4 

The  number  of  visits  to  the  normal  flowers  was  nearly  four  times  as 
great  as  to  those  with  the  petals  shortened.  Since  conditions  were  other- 
wise identical,  this  not  only  proves  the  importance  of  the  corolla  in  attrac- 
tion, but  also  shows  that  its  effectiveness  is  related  to  its  expanse.  The  14 
inspections  were  made  by  Apis  and  Bombus  and  indicate  that  about  one- 
fourth  of  the  visits  failed  because  of  the  disturbance  of  the  usual  perception. 
This  was  especially  true  of  B.  juxtus,  which  flew  away  in  7  different  cases 
when  only  a  centimeter  from  the  flower.  Moreover,  Apis  was  forced  to 
change  its  method  of  working,  since  it  could  no  longer  walk  around  the 
stamen  mass  on  the  petals. 

Stamens  covered. — The  stamens  were  covered  with  absorbent  cotton 
in  30  flowers  and  an  equal  number  of  normal  ones  taken  for  comparison. 
Apis  visited  25  of  the  latter,  but  found  the  stamens  in  only  one  of  those 


30 


NORMAL  AND  EXPERIMENTAL  POLLINATION. 


covered,  though  it  hovered  low  over  3  others.  Bombus  occidentalis  went  to 
7  normal  flowers  and  hovered  over  2  of  the  changed  ones,  while  for  B.  juxtus 
the  numbers  were  8  and  1  respectively. 

ARTIFICIAL  AND  PAINTED  FLOWERS. 
Crepe-paper  corollas. — In  all  the  flowers  employed  the  anthers  were 
just  beginning  to  dehisce,  as  flowers  at  this  stage  had  been  found  to  be  most 
attractive  to  insects.  Other  open  flowers  nearby  were  removed,  so  that 
they  would  not  attract  visitors  from  the  group  under  observation.  After 
the  petals  and  sepals  were  removed,  artificial  corollas  of  red,  blue,  yellow, 
or  white  crepe-paper  were  wired  below  the  anthers.  A  normal  flower 
was  left  for  comparison  near  each  artificial  one,  3  flowers  of  each  color 
being  used  in  the  experiment,  making  a  total  of  15  for  each  of  the  two  lands. 
Table  11  shows  the  response  to  them,  as  well  as  the  color  preferences. 

Table  11. — Visits  to  natural  and  paper  flowers. 


Species. 


Normal. 


Red. 


Green.    1    White. 


Bombus  juxtus 

morrisoni.  .  .  , 
Andrena  vicina 

crataegi 

prunorum .  .  , 
Acmaeops  longicornis . 

Osmia  bruneri 

phaceliae 

Prosopis  wootoni 

varifrons .  .  . 

basalis 

Pipiza  sp 

Diptera 


100 

7 

25 

2 

1 

17 

18 

1 

14 

10 

2 

1 


Total . 


4:31 


The  visits  to  normal  flowers  were  six  times  as  many  as  to  the  artificial 
ones.  While  the  bees  clearly  avoided  the  imitations  as  a  whole,  there 
was  a  great  difference  in  response  to  the  various  colors.  The  visits  to  green, 
white,  and  red  were  negligible. 

Artificial  corollas  similar  to  those  used  in  the  previous  experiment  were 
made  of  crepe-paper,  but  with  the  petals  fringed  by  cutting  them  length- 
wise. Four  artificial  flowers  of  each  color  and  16  normal  flowers  were  used. 
Observations  from  8  to  10  a.m.  on  the  first  morning  and  from  8  to  9  a.m. 
on  the  second  gave  the  results  shown  in  table  12. 

Of  222  visits,  only  18  were  made  to  the  artificial  flowers,  chiefly  by  Bombus 
and  Osmia,  a  fly  being  the  only  other  visitor  to  them.  It  is  significant 
that  Apis  did  not  go  to  a  single  imitation.  While  the  numbers  are  too 
small  to  be  of  much  value,  it  is  interesting  to  note  that  blue  and  yellow 
were  again  the  preferred  colors. 

Painted  corollas. — When  the  petals  were  painted  blue,  green,  or  yellow 
with  water-colors,  Bombus  juxtus  visited  as  many  painted  as  normal  flowers, 
in  contrast  to  the  ratio  of  11:1  for  natural  and  paper  flowers.  Andrena 
crataegi  went  only  to  the  blue  flowers,  in  addition  to  the  normal  ones. 


RUBUS    DELICIOSUS.  31 

Table  12. — Visits  to  natural  flowers  and  flowers  with  fringed  paper  corollas. 


Species. 


Normal.         Red.         Yellow.        Green.  Blue 


Apis  mellifica 

Bombus  bifarius .  . 

juxtus.  . . 

proximus . 
Andrena  crataegi . 
Osmia  phaceliae .  . 
Musca  sp 


Total. 


Bombus  proximus.  . .  . 

bifarius 

Andrena  crataegi .... 

madronitens. 
Syrphus  amerieanus.  . 
Halictus  pulzenus.  .  .  . 

Prosopis  elliptica 

Musca  sp 


Total . 


106 
39 
12 


0 

o 

1 

0 

0 

0 

0 

0 

0 

0 

0 

0 

2 

0 

2 

1 

ADDITION  OF  HONEY  AND  ODOR. 

Honey. — In  this  installation  one-third  of  the  flowers  were  supplied  with 
a  drop  of  honey  at  the  base  of  the  filaments,  another  third  with  a  drop  at  the 
center  of  the  stamen  mass,  and  the  remainder  were  left  normal.  Halictus 
pulzenus  visited  4  normal  flowers  and  10  with  honey  at  the  filament  base. 
Andrena  crataegi  visited  but  one  flower  of  this  sort;  it  actually  landed  at 
others  but  flew  away  at  once,  as  did  Bombus  proximus.  The  total  number 
of  visits  to  normal  flowers  was  46,  in  contrast  to  11  for  those  with  honey 
added,  giving  a  ratio  of  4:1. 

SUMMARY. 

A  comparison  of  the  tables  obtained  from  the  various  calendars  not  only 
reveals  the  differences  arising  out  of  time  and  place,  but  also  throws  light 
upon  discrepancies  between  the  results  of  different  observers  and  investi- 
gators, making  it  clear  that  comparison  is  often  misleading  if  not  impossible 
when  different  years  and  regions  are  concerned.  There  was  much  difference 
in  the  number  of  visits  on  successive  days  in  the  same  spot,  and  a  marked 
one  when  different  portions  of  the  flowering  period  were  concerned,  arising 
chiefly  out  of  the  period  of  flight  for  the  various  genera.  Neighboring 
areas  likewise  showed  a  distinct  divergence,  which  was  strikingly  evident  in 
the  ratios  of  visits  for  the  bees,  namely,  Apis  1:6,  Bombus  17:1,  Andrena 
7:1,  and  Osmia  3: 1. 

The  decisive  effect  of  cutting  the  petals  back  to  half  their  length  is  espe- 
cially significant  in  connection  with  the  question  sometimes  raised  as  to 
the  value  of  the  corolla  in  attraction.  Covering  the  stamens  excluded 
visits  entirely  and  suggests  that  insects  distinguish  clearly  between  the 
corolla  and  the  stamen  mass,  or  at  least  readily  recognize  that  the  latter  is 
changed.     Although  49  visits  were  made  to  paper  flowers  of  various  colors, 


32 


NORMAL  AND  EXPERIMENTAL  POLLINATION. 


this  was  less  than  one-eighth  of  the  number  paid  to  natural  ones  at  the  same 
time.  All  the  colors  received  visits,  as  follows :  red  3,  yellow  22,  green  3, 
blue  17,  white  4.  In  accordance  with  the  general  rule,  painted  flowers 
were  visited  much  more  than  paper  ones,  doubtless  owing  to  the  fact  that 
they  differed  but  little  from  the  normal  ones,  as  shown  especially  by  the 
behavior  of  Bombus.  The  attractive  power  of  honey  was  again  found  to  be 
slight,  flowers  with  honey  receiving  but  one  visit  to  4  for  the  normal  ones. 

RUBUS  STRIGOSUS. 
NORMAL  POLLINATION. 
Habit  and  structure. — These  flowers  open  later  than  those  of  Rubus 
deliciosus,  but  the  two  are  in  bloom  together  for  a  considerable  period. 
They  are  quite  inconspicuous  because  of  their  small  size  and  recurved 
petals  and  the  scattered  position  among  the  leaves.  However,  the  large 
amount  of  easily  available  nectar  makes  this  species  very  attractive  to 
several  kinds  of  insects.  The  nectar  is  formed  within  the  stamen  circle 
at  the  base  of  the  ovaries.  It  oozes  out  in  drops  and  if  not  kept  lapped  up 
by  the  bees,  the  depressed  ring  becomes  filled  with  it.  In  order  to  find  out 
how  rapid  this  flow  of  nectar  is,  4  plants  profuse  with  flowers  were  covered 
with  paper  bags  in  the  evening,  so  that  no  visitors  could  get  nectar  until 
the  flowers  were  examined.  At  9  the  next  morning,  when  the  visits  of  the 
bees  were  becoming  numerous,  the  bags  were  removed.  Flowers  outside 
the  bag,  which  had  been  receiving  the  morning  visitors,  showed  only  the 
glistening  droplets  of  nectar,  while  a  full  nectar  ring  was  very  conspicuous 
in  all  the  bagged  flowers  mature  enough  to  produce  it  (plate  3). 

Behavior. — A  pis  mellifica  hangs  suspended  from  the  flowers  while 
sucking  nectar.  It  scrapes  pollen  from  its  head  and  thorax  with  the 
second  pair  of  legs  on  to  the  corbiculse  of  the  third  pair.  One  individual 
flew  half  an  inch  above  flowers  with  dry  anthers  and  discovered  without 
landing  that  there  was  no  nectar.  Prosopis  episcopalis  goes  to  open  flowers 
for  nectar  and  lands  on  the  petals.  If  the  petals  are  closed,  it  goes  around 
the  edge  of  the  bud  and  inserts  its  ligule  between  the  petals.  The  normal 
visitors  on  3  successive  days  during  periods  of  2  hours  to  100  open  flowers 
are  listed  in  table  13. 

Table  13. — Visitors  on  three  successive  days. 


Species. 

June 
29. 

June 
30. 

July 
1. 

Species. 

June 
29. 

June 
30. 

July 
1. 

34 
0 
0 
2 
0 
1 

118 
6 
8 
8 
3 
0 

47 
15 
15 
7 
3 
0 

Andrena  crataegi 

0 
0 
1 

2 

0 
2 
4 
0 

1 
0 
2 
0 

Bombus  bifarius 

juxtus 

proximus 

Andrena  vicina 

madronitens. . 

Prosopis  episcopalis. .  .  . 
Monumetha  albifrons.  . 

Total 

40 

149 

90 

Rubus  strigosus  is  primarily  a  honey-bee  flower,  as  is  shown  by  the  fact 
that  199  of  the  279  visits  were  made  by  Apis;  of  the  remaining  80  visits, 
61  were  made  by  Bombus. 


ROSA  ACICULARIS.  33 

No  previous  floral  study  of  Rubus  has  been  made  in  America,  but  several 
European  species  have  received  much  attention  (Knuth,  1908:352). 

EXPERIMENTS. 

MUTILATION. 

Floral  envelopes  or  stamens  removed. — Apis  mellifica  started  to 
land  at  a  flower  with  the  stamens  removed,  but  flew  away.  The  nectar 
was  clearly  visible,  but  the  excision  of  the  stamens  changed  the  appearance 
of  the  flowers  so  much  that  it  seemed  to  frighten  this  bee.  Andrena 
madronitens  worked  at  flowers  with  the  calyx  and  corolla  or  stamens  gone 
as  at  normal  flowers.  Prosopis  episcopalis  stopped  at  one  with  the  stamens 
and  corolla  removed  and  worked  as  usual,  while  Osmia  bruneri  visited  a 
flower  with  the  perianth  gone.  These  results  are  opposed  to  those  obtained 
with  Rubus  deliciosus,  but  this  is  readily  explained  by  the  difference  in 
the  size  and  visibility  of  the  petals.  In  strigosus  these  are  not  only  several 
times  smaller  than  in  deliciosus,  but  their  position  further  decreases  their 
attractiveness. 

ROSA  ACICULARIS. 

NORMAL  POLLINATION. 

Habit  and  structure. — The  corolla  of  Rosa  is  pink  in  color  and  widely 
expanded,  forming  a  broad  landing- platform  and  a  bright  disk  of  color, 
evidently  visible  to  insects  from  some  distance.  The  stamens  are  numerous 
and  the  pollen  abundant.  A  mild  sweet  odor  adds  to  the  apparent  attrac- 
tiveness of  the  flower. 

Behavior. — Bombus  edwardsi  tumbles  about  the  stamens  very  rapidly, 
collecting  pollen  in  the  corbiculae,  on  the  mouth-parts,  and  the  hairs  of 
the  abdomen.  Pollen  was  gathered  at  Rubus  deliciosus  in  much  the  same 
manner,  and  this  bee  goes  from  Rosa  to  Rubus  or  the  reverse  without 
showing  a  preference  for  either.  It  did  not  stop  at  flowers  in  which  the 
stamens  and  pistils  were  covered  by  the  unfolding  petals,  but  went  on  to 
the  next  open  flower.  The  anthers  in  Rosa  are  not  mature  when  the  petals 
are  unfolding  and  the  bee  has  perhaps  learned  by  experience  that  the  pollen 
is  not  available  until  the  petals  are  broadly  expanded.  One  individual  of 
Bombus  flavifrons  endeavored  to  open  a  half-expanded  flower,  landing  on 
the  lower  petal  and  trying  to  push  its  head  in,  but  after  making  several 
unsuccessful  attempts  it  flew  away.  B.  bifarius  tramples  back  and  forth 
among  the  stamens  collecting  pollen,  the  tip  of  its  abdomen  at  the  same  time 
rubbing  the  stigmatic  surfaces  and  depositing  pollen  previously  collected. 
B.  proximus  collects  pollen  on  the  rose;  it  files  low  above  flowers  which  are 
opening  but  lands  only  on  those  with  dehiscing  anthers. 

Andrena  crataegi  collects  pollen  most  industriously,  even  visiting  flowers 
with  petals  gone  and  stamens  brown,  trying  to  get  pollen  from  the  withered 
anthers.  Andrena  vicina  tramples  rapidly  over  the  stamen  mass,  going 
round  and  round  with  its  head  buried  among  the  anthers.  The  first  two 
pairs  of  legs  gather  pollen  and  pack  it  on  the  third  pair.  A.  madronitens 
arches  the  tip  of  its  abdomen  downwards  toward  its  head,  inclosing  a 
group  of  stamens.     While  in  this  position,  it  collects  pollen  rapidly  with 


34 


NORMAL  AND  EXPERIMENTAL  POLLINATION. 


the  front  legs  and  stores  it  on  the  hind  ones.  Prosopis  elliptica  works 
very  rapidly  with  its  mouth-parts  and  with  the  front  pair  of  legs.  It 
opens  the  anther  with  the  front  legs,  scrapes  out  pollen,  and  also  picks 
it  up  from  the  corolla.  Anthophora  simillima  poises  7  to  15  cm.  above  the 
flower,  meanwhile  buzzing  loudly,  and  then  makes  a  dive  for  it.  While 
diving,  head  and  abdomen  tip  are  together,  and  as  it  lands  it  grasps  the 
stamens  with  its  front  legs  and  slides  down  the  bunch  of  filaments.  When 
the  anthers  are  reached,  a  struggling  movement  takes  place,  during  which 
pollen  is  put  on  the  third  pair  of  legs,  when  it  buzzes  into  the  air  again  and 
dives  for  another  flower.  It  often  darts  repeatedly  into  the  same  flower, 
apparently  getting  some  nectar  during  this  process.  Monumetha  albifrons 
tramples  around  on  the  stamens  with  its  head  buried  in  the  mass.  It  moves 
very  rapidly,  working  all  three  pairs  of  legs  and  storing  the  accumulated 
pollen  on  its  ventral  scopa.  The  latter  also  rubs  rapidly  against  the  anthers 
and  collects  pollen.  Osmia  bruneri  tramples  over  the  stamens  in  the  same 
manner  as  Bombus.  Megachile  wootoni  moves  around  very  rapidly  while 
on  the  stamens,  the  first  two  pairs  of  legs  scraping  out  the  pollen  and  passing 
it  to  the  third  pair,  which  place  it  on  the  scopa.  This  is  raised  in  the  air 
and  usually  does  not  come  in  contact  with  the  anthers. 

Table  14  shows  the  visitors  observed  during  30  minutes  on  42  flowers  of 
Rosa,  14  of  which  were  just  opening  and  the  anthers  beginning  to  dehisce. 
The  lists  were  made  on  successive  days,  and  exhibit  the  difference  often  to  be 
expected. 

Table  14. — Visitors  to  normal  flowers. 


Species. 

Visitors. 

Visitors 
and  visits. 

Species. 

Visitors. 

Visitors 
and  visits. 

Bombus  bifarius.  .  .  . 

proximus . . . 

juxtus 

occidentalis. 
Andrena  crataegi.  .  . 

vicina 

18 
7 
0 
0 

14 
1 

0:0 
0:0 
3:5 
1:2 
4:4 
0:0 

Halictus  pulzenus. .  . 
Prosopis  elliptica.  .  . 
Megachile  wootoni. . 
Syrphus  sp 

Total 

3 
2 
0 
2 

0:0 
1:2 
3:3 
0:0 

47 

12:16 

The  pollination  of  the  rose  appears  to  have  received  no  attention  in  this 
country,  but  several  species  have  been  studied  in  Europe  (Knuth,  1906:348). 
These  are  chiefly  visited  by  beetles,  though  several  genera  of  bees  have 
been  taken  on  R.  canina,  and  two  species  of  Bombus  on  rubiginosa. 

EXPERIMENTS. 

MUTILATION. 
Corolla  shortened. — The  petals  of  Rosa  were  cut  to  half  their  length, 
giving  the  corolla  a  rotate  form.  This  made  them  paler  in  color,  as  the 
petals  are  almost  white  toward  the  base.  Since  the  flower  is  smaller,  the 
stamens  also  become  more  conspicuous.  At  such  flowers,  Bombus  juxtus 
landed,  collected  some  pollen  and  then  passed  on  to  the  next,  never  securing 
all  of  the  available  pollen  at  any  flower.  Monumetha  albifrons  remained 
at  each  flower  a  long  time  and  collected  much  pollen.     In  order  to  determine 


ROSA  ACICULARIS. 


35 


the  comparative  effect  of  reducing  the  attractive  surface  of  the  corolla, 
10  such  flowers  were  grouped  with  10  normal  ones.  Table  15  shows  the 
visitors  during  an  hour  of  observation. 

Table  15. — Visitors  to  normal  and  reduced  flowers. 


Species. 

Normal. 

Reduced. 

21 
8 
8 
3 
1 
1 
0 

9 

1 
2 
0 
0 
0 

occidentalis 

Anthophora  simillima 

prunorum 

Total 

42 

13 

In  accordance  with  the  rule,  the  reduction  of  the  corolla  surface  greatly 
decreased  the  attractiveness  of  the  rose,  since  there  were  three  times  as 
many  visitors  to  the  normal  flowers. 

Stamens  masked. — The  stamens  of  10  flowers  were  masked  with  a 
veil  of  cotton  and  10  normal  blossoms  left  for  comparison.  Two  hours  of 
observation  gave  the  results  shown  in  table  16. 

Table  16. — Visits  to  normal  and  masked  flowers. 


Species. 

Normal. 

Masked. 

Andrena  madronitens 

2 
2 

3 

1 
1 
1 

0 
0 
0 
0 
0 
0 
0 

Anthophora  simillima 

Syrphus  americanus 

Total 

12 

1 

Andrena  madronitens  landed  on  the  veil  of  cotton,  walked  over  it,  and 
finally  slipped  under  the  edge  to  the  stamens.  A  second  bee  tried  the 
same  method,  but  failed  to  find  them.  Bombus  proximus  and  3  individuals 
of  B.  bifarius  inspected  the  masked  flowers,  but  did  not  stop  at  them. 
Where  the  cotton  had  slipped  a  little  at  the  edge  exposing  the  stamens, 
proximus  landed  in  the  flower,  but  its  legs  became  tangled  in  the  cotton 
and  it  flew  away  as  though  frightened. 

ARTIFICIAL  AND  PAINTED  FLOWERS. 

Crepe-paper  corollas. — The  corollas  were  replaced  by  artificial  ones 

of  red,  green,  and  yellow  crepe-paper,  resembling  the  normal  in  size  and 

form.     The  crepe  flowers  were  paired  with  normal  ones  in  the  various 

positions  on  the  bush.     Bouquets  of  flowers  in  bottles  of  water  were  sus- 


36 


NORMAL  AND  EXPERIMENTAL  POLLINATION. 


pended  from  the  branches  to  increase  the  number  of  normal  flowers  under 
observation.  One  Halictus  pulzenus  went  to  all  flowers,  making  no  dis- 
tinction between  the  normal  and  those  with  artificial  corollas.  Another 
individual  visited  one  yellow,  two  green,  and  many  normal  flowers.  Bombus 
proximus  went  to  118  normal  flowers  and  only  18  with  crepe  corollas, 
Syrphus  americanus  to  3  yellow,  2  green,  and  11  normal,  and  Clisodon 
terminalis  to  18  normal  and  1  white  crepe  flower. 

The  results  of  observations  made  on  another  day  are  given  in  table  17, 
which  shows  the  visits  to  normal  and  crepe  flowers  during  an  hour.  Eight 
natural  flowers  were  used,  together  with  4  of  each  color,  making  20  artificial 
flowers  in  all. 


Table  17. 

—Visits  to  natural  and  artificial  flowers. 

Species. 

Normal. 

Violet. 

Red. 

Blue. 

White. 

Green. 

20 
19 
19 
2 

0 
0 
0 

1 

0 
0 
1 
0 

0 
0 
0 
0 

0 
1 
0 
0 

0 
0 
0 
0 

Total ...                     

60 

1 

1 

0 

1 

0:3 

Later,  Bombus  proximus  and  juxtus  visited  these  bushes  several  times, 
but  stopped  only  at  the  natural  flowers,  passing  by  the  artificial  corollas. 
The  first  stopped  twice  at  a  petal  lying  on  some  leaves  and  examined  it, 
but  did  not  land  at  any  of  the  artificial  flowers  in  passing  from  one  natural 
flower  to  others  more  distant. 

ADDITION  OF  HONEY  AND  ODOR. 

Honey. — Diluted  honey  was  placed  in  the  center  of  the  stamen  group, 
so  that  visitors  coming  for  either  pollen  or  nectar  would  be  sure  to  come  in 
contact  with  it.  This  glistened  in  the  sunlight  and  was  distinctly  visible 
3  meters  away  from  the  flowers.  In  general,  Bombus  proximus  avoided 
flowers  treated  in  this  way,  and  when  it  did  land  usually  paid  no  attention 
to  the  honey.  When  this  was  noticed,  the  bee  flew  away  suddenly,  or 
avoided  it  and  trampled  among  the  anthers  on  the  other  side  of  the  flower. 
One  individual  landed  at  a  flower  with  diluted  honey,  commenced  at  once 
to  sip  nectar,  and  stayed  for  a  long  time.  It  flew  away  for  a  second,  came 
back  again,  and  took  more  nectar.  This  bee  went  to  the  next  flower  which 
was  normal  and  trampled  among  the  stamens  in  the  usual  fashion.  No 
pollen  was  collected  in  the  next  two  flowers  with  honey- drops,  but  the  bee 
secured  nectar.  Three  normal  flowers  were  then  visited  in  succession  and 
at  each  it  trampled  among  the  stamens  and  collected  pollen.  Monumetha 
albifrons  sipped  honey  for  60  seconds  on  a  flower  that  had  pure  honey-drops 
on  the  stamens.  It  also  went  to  those  in  which  the  honey-drops  were 
diluted,  but  showed  no  preference  for  either  kind. 

Twenty  flowers  of  each  kind  were  used  in  the  following  experiment  to 
find  out  whether  honey  would  prove  an  added  attraction  to  visitors;  the 
period  of  observation  was  an  hour. 


ROSA   ACICULARIS.  37 

Table  18. — Visits  to  normal  flowers  and  those  with  honey  on  the  stamens. 


Species. 

Visitors. 

Normal 

flowers. 

1 
Honey  flowers. 

Pollen. 

Nectar. 

15 
4 
3 
2 

1 

54 
1 
0 
2 
1 

36 
4 
3 
0 
0 

5 
0 
0 
0 
0 

Total 

25 

58 

43 

5:48 

The  results  indicate  that  the  honey  did  not  constitute  an  added  attraction, 
except  possibly  to  Prosopis  and  Andrena. 

Diluted  honey  was  put  on  the  stamens  of  half  the  flowers  employed  in 
experiment  1,  while  in  experiment  2  the  honey  was  placed  in  a  circle  around 
the  base  of  the  filaments  and  an  additional  drop  at  the  center  of  the  stamen 
mass;  10  normal  and  10  honey  flowers  were  used  in  each  case,  and  the  obser- 
vation period  was  2  hours. 

Table  19. — Visitors  to  normal  and  honey  floivers. 


Species. 

Experiment  1. 

Experiment  2. 

Normal 
flowers. 

Honey 

on 
stamens. 

Normal 
flowers. 

Honey 

under 

stamens. 

17 
0 
1 
0 
6 
0 

3 
0 
0 

0 
0 

1 

13 
5 
0 
1 
0 
0 

27 
1 
0 
2 
0 
0 

Total 

24 

4 

19 

30 

Placing  honey  on  the  stamens  reduced  the  number  of  visitors  very  greatly, 
the  ratio  being  24 : 4.  This  was  due  to  interference  with  the  usual  collection 
of  pollen.  When  the  honey  was  placed  at  the  base  of  the  filaments,  the 
visits  of  Bombus  juxtus  were  likewise  reduced,  but  those  of  B.  proximus 
were  doubled,  without  an  evident  reason.  However,  it  landed  and  took 
honey  in  but  10  of  these,  leaving  the  others  immediately  after  alighting, 
as  though  disturbed  by  the  presence  of  the  honey. 

Honey  and  talcum  powder. — Flowers  were  modified  by  the  addition 
of  pure  or  diluted  honey,  or  talcum  powder  of  the  "Love  me"  and  "Arbutus" 
brands.  There  were  10  of  each  type  of  modified  flowers  used  and  40  normal 
ones  were  paired  with  them  for  comparison.  Of  the  49  visitors,  30  went  to 
normal  flowers,  4  to  flowers  with  pure  honey,  8  to  flowers  with  diluted 
honey,  5  to  those  with  "Love  me"  sachet,  and  2  to  those  with  "Arbutus" 


NORMAL  AND  EXPERIMENTAL  POLLINATION. 


sachet.  Clisodon  terminalis  flew  above  the  flowers  scented  with  "Arbutus" 
powder  for  some  little  time  before  landing,  projecting  its  ligule,  which  was 
not  its  normal  procedure  when  hovering  above  flowers.  One  Bombus 
juxtus  landed  on  flowers  powdered  with  both  kinds  of  sachet,  but  quickly 
flew  away.  Syrphus  opinator  alighted  on  some  with  "Love  me"  sachet 
on  them  and  worked  as  usual.  It  also  landed  on  flowers  with  honey-drops 
but  did  not  find  the  honey. 

Camphor. — The  response  of  the  various  species  to  flowers  in  which 
powdered  "moth  balls"  had  been  sprinkled  on  the  stamens  and  to  normal 
flowers  is  shown  in  table  20. 

Table  20. — Visitors  to  normal  flowers  and  flowers  scented  with  camphor. 


Species. 

Normal 
flowers 

Scented 
flowers 

Species. 

Normal 
flowers. 

Scented 
flowers. 

Bombus  proximus 

35 
2 
6 
2 
5 

23 
1 
1 
1 
3 

Halictus  pulzenus 

Monumetha  albifrons .... 
Anthophora  simillima .... 
Syrphus  opinator 

Total 

3 

2 
1 

1 

0 

2 
0 
0 

Prosopis  elliptica 

Andrena  crataegi 

57 

31 

It  is  somewhat  surprising  to  find  that  the  flowers  with  an  unpleasant 
odor  attracted  half  as  many  visitors  as  the  normal  ones,  but  this  is  probably 
to  be  explained  on  the  basis  of  habit. 

Cotton  perfumed  with  anise  was  wound  around  the  pedicels  under  the 
sepals  in  8  pairs  of  flowers,  normal  flowers  adjoining  the  scented  ones 
in  each  case,  and  the  observations  covering  an  hour.  The  response  to 
anise  was  essentially  the  same  as  that  to  camphor. 

Table  21. — Visitors  to  normal  and  anise-scented  flowers. 


Species. 

Normal. 

Anise. 

Species. 

Normal. 

Anise. 

27 
9 
5 
5 
4 
3 

14 
4 
0 
0 
5 
2 

2 
0 
0 

1 
0 

occidentals 

Monumetha  albifrons.  .  .  . 
Andrena  crataegi 

Syrphus  americanus 

Prosopis  elliptica 

Eristalis  latifrons 

Total 

58 

28 

SUMMARY. 

As  would  be  expected  from  their  similar  size  and  structure,  the  rose  and 
salmonberry  yielded  much  the  same  experimental  results.  The  reduction 
of  the  corolla  decreased  the  visits  to  the  one  3  and  to  the  other  4  times,  while 
in  both  cases  flowers  with  stamens  masked  obtained  but  few  visits.  The 
visitors  to  paper  flowers  were  much  more  numerous  in  the  case  of  Rubus, 
but  this  was  probably  due  in  part  at  least  to  the  more  extensive  experiments 
with  it.    The  reverse  was  true  in  the  case  of  flowers  with  added  honey,  the 


GERANIUM    CAESPITOSUM.  39 

roses  thus  treated  receiving  a  relatively  large  number  of  visitors.  The 
difference  between  the  two,  however,  was  almost  wholly  a  consequence  of 
the  preference  of  Bombus  proximus  for  the  honey-flowers  of  the  rose.  The 
addition  of  various  odors  to  flowers  of  the  rose  regularly  decreased  the 
number  of  visitors  about  half,  quite  irrespective  of  whether  the  odor  was 
one  ordinarily  regarded  as  pleasant.  It  seems  evident  that  this  decrease 
was  due  to  the  strange  odor  disturbing  the  habitual  response  of  the  pol- 
linators. 

GERANIUM  CAESPITOSUM. 
NORMAL  POLLINATION. 
Habit  and  structure. — The  flowers  of  Geranium  are  regular  and  the 
five  nectaries  are  so  placed  that  the  nectar  in  all  is  equally  exposed  and 
accessible.  All  the  visitors  except  Halictus  sp.  usually  come  for  nectar. 
The  inner  row  of  anthers  dehisce  first,  followed  by  the  outer  row  from 
10  to  24  hours  later  (plate  7). 

Behavior. — Bombus  juxtus  lands  on  the  disk-shaped  corolla  and  proceeds 
to  circle  the  stamen  group,  taking  nectar  at  each  of  the  nectaries.  It 
secures  nectar  from  flowers  in  which  all  the  anthers  have  dropped  off, 
indicating  that  the  flow  continues  while  the  stigmatic  surface  is  receptive. 
A  few  individuals  are  satisfied  to  suck  nectar  from  only  one  or  two  nectaries 
at  each  flower,  and  B.  bifarius  usually  stops  likewise  at  only  a  few  of  those 
in  each  flower,  instead  of  making  the  complete  round.  Halictus  pulzenus 
comes  for  both  nectar  and  pollen.  It  visits  each  of  the  5  nectaries,  some- 
times going  around  the  circle  twice  in  succession.  After  getting  all  the 
nectar  available,  it  walks  up  the  anthers,  scrapes  out  pollen  with  its  front 
legs,  and  packs  it  on  the  hind  ones.  This  bee  is  so  small  that  it  can  stand 
under  the  outwardly  curved  anthers.  When  in  this  position,  pollen  falls 
on  its  back,  but  it  touches  the  stigma  only  as  it  flies  away.  Halictus  was 
seen  to  pick  up  the  pollen  that  had  fallen  on  the  corolla,  brush  its  head  well 
with  the  front  legs,  and  then  eat  the  pollen.  Prosopis  elliptica  has  a  shiny 
body  on  which  pollen  does  not  collect  easily.  It  is  so  small  that  in  dipping 
into  the  nectaries  only  the  lower  shorter  row  of  anthers  or  the  recurved 
styles  touch  its  abdomen.  This  species  is  probably  not  a  very  effective 
pollinator  on  this  account. 

Andrena  madronitens  is  a  pollen  collector.  It  hangs  suspended  from  the 
styles  and  filaments,  and  moves  around  them  repeatedly,  gathering  pollen. 
It  collects  with  its  mouth  and  front  legs  and  places  the  pollen  on  the  hind 
ones.  Monumetha  albifrons  lands  with  its  head  pointing  toward  the  nec- 
taries. It  tips  its  abdomen  upward  as  it  goes  from  nectary  to  nectary,  and 
this  gives  it  the  appearance  of  standing  on  its  head.  The  tip  of  its  abdomen 
rubs  the  anthers  as  it  sucks  nectar.  A  pis  mellifica  stops  at  all  the  nectaries 
and  makes  no  effort  to  get  pollen.  The  thoracic  hairs  become  covered  with 
the  latter  and  scrape  the  anthers  and  style,  dusting  them  with  pollen  as  it 
moves  about  the  nectar  circle.  Osmia  bruneri  and  Sphex  vulgaris  also  visit 
each  nectary,  where  they  appear  to  be  standing  on  their  heads.  The  head 
of  the  latter  is  hairy  and  serves  to  collect  and  deposit  pollen.  Pseudomasaris 
vespoides  likewise  goes  to  each  nectary,  the  dorsal  surface  of  the  bee  touching 
the  anthers  in  one  flower  and  the  stigmas  in  the  next. 


40 


NORMAL  AND  EXPERIMENTAL  POLLINATION. 


Merritt  (1896:149)  has  studied  the  pollination  of  the  closely  related 
Geranium  richardsoni  in  California,  where  the  most  frequent  visitors  are 
able  to  secure  nectar  without  touching  anthers  or  stigmas.  However, 
larger  bees  also  visit  the  flowers,  namely,  Apis,  Anthophora,  Coelioxys, 
Osmia,  and  Bombus  californicus,  and  these  readily  effect  pollination  as  they 
cling  to  the  anthers  or  styles.  Robertson  (1889:229;  1893:272)  briefly 
describes  the  behavior  of  the  flower  in  G.  maculatum  and  G.  carolinianum 
and  gives  a  list  of  the  visitors  to  each.  The  insect  visitors  of  a  large  number 
of  European  species  are  given  by  Knuth  (1908:218). 

CALENDARS. 

Fifty  flowers  were  under  observation  on  each  of  the  five  days  for  which 
the  visitors  are  given  in  table  22. 


Table  22. — Visitors  to  normal  flowers. 


Species. 


June  28, 
30  min. 


June  29, 
120  min. 


Aug.  17, 
80  min. 


Aug.  19, 
60  min. 


Aug.  20, 
45  min. 


Apis  mellifica 

Ancistrocerus  sp 

Bombus  juxtus 

Coelioxys  maesta 

Colletes  sievisiti 

Halictus  pulzenus 

(Lasioglossum)  sp 

Monumetha  albifrons 

Prosopis  basalis 

varifrons 

wootoni 

Pseudomasaris  vespoides. . 

Sphex  vulgaris 

Thanaos  martialis 

Muscidae 

Coleoptera 

Total 


Table  23. — Visitors  and  visits  to  normal  flowers. 


Species. 


July  16.  July  16 


July  25. 


Bombus  bifarius 

juxtus 

proximus. . .  . 
Andrena  madronitens 

Colletes  sieverti 

Halictus  pulzenus.  .  .  . 
Megachile  texana.  .  .  . 
Monumetha  albifrons 
Prosopis  elliptica 

varifrons. . .  . 
Syrphus  opinator 

Total 


10:186 

6:44 

4:45 

22:97 

1:1 

2:5S 

0:0 

0:0 

0:0 

3:3 

2:2 

2:2 

0:0 

2:2 

0:0 

0:0 

0:0 

1:1 

9:13 

1:1 

1:1 

1:1 

27:24S 


0:0 

5:36 

0:0 

1:2 

0:0 

0:0 

0:0 

1:1 

0:0 

0:0 

0:0 


7:39 


GERANIUM    CAESPITOSUM. 


41 


In  the  columns  for  July  16,  40  flowers  were  under  observation  for  the  two 
successive  hour  periods.  On  July  25,  only  26  flowers  were  in  the  group 
observed  during  an  hour  period. 

As  would  be  expected,  the  records  for  two  successive  hours  resemble 
each  other  closely,  but  depart  much  more  widely  from  that  made  a  number 
of  days  later.  This  record  contains  but  three  of  the  species  present  on 
July  16,  and  the  number  of  visitors  and  visits  is  very  low.  The  inversion 
of  the  number  for  Bombus  bifarius  and  juxtus  is  the  most  striking  feature  of 
the  two  successive  records.  In  table  23  the  most  important  fact  is  the 
change  of  dominance  from  Prosopis  at  the  opening  of  the  flowering  period 
to  Bombus  and  Halictus  near  the  close.  This  is  to  be  explained  by  the 
fact  that  the  latter  were  working  on  preferred  species  earlier  and  went  to 
Geranium  in  abundance  only  when  their  choice  became  more  restricted. 
This  is  likewise  the  explanation  of  the  doubling  of  the  average  number  of 
visitors  per  hour  period  in  the  later  observations. 

EXPERIMENTS. 

CHANGE  OF  POSITION. 

Flowers  vertical  or  inverted. — When  the  face  of  the  flower  was  turned 
so  that  it  was  vertical,  Bombus  juxtus  found  no  difficulty  in  hanging  on, 
and  its  behavior  was  practically  the  same  as  at  a  normal  flower.  In  the 
case  of  inverted  flowers,  however,  it  experienced  much  trouble  in  keeping  a 
foothold.  One  individual  landed  on  the  bottom  of  the  flower,  which  was 
then  uppermost,  went  over  the  edge  to  the  face,  but  finally  flew  away  with- 
out securing  nectar.  Another  went  to  an  inverted  flower  that  was  half- open, 
but  did  not  succeed  in  opening  it.  It  next  went  to  another  half-open 
inverted  flower,  landing  on  the  calyx  and  looking  for  the  opening  to  the 
nectaries  among  the  sepals,  and  departed  unsuccessful. 

MUTILATION. 

Cotton  over  nectaries. — A  circle  of  cotton  was  placed  at  the  base  of  the 
filaments  so  that  it  covered  the  opening  to  the  nectaries.  One  individual 
of  Prosopis  varifrons  flew  around  above  the  flowers  without  landing.  Another 
individual  alighted  and  poked  around  the  edges  of  the  cotton,  but  did  not 
find  the  nectaries.  A  fly  also  landed  and  pushed  out  its  ligule,  but  was 
unable  to  locate  the  nectar.  Bombus  juxtus  secured  nectar  from  7  flowers 
by  pushing  aside  the  edge  of  the  cotton  until  the  nectary  was  exposed. 

Table  24. — Visitors  to  normal  and  mutilated  floivers. 


Specie?. 

Normal 
flowers. 

Petals 
removed. 

Petals 

and 

sepals 

removed. 

Stamens 
removed. 

Stamens 
and 
style 

removed. 

15 
5 
0 

10 

1 
0 
0 
0 

1 
1 
0 
0 

15 
4 
3 
0 

12 
3 
2 
5 

Apis  mellifica 

Total 

30 

1 

2 

22 

22:47 

42 


NORMAL  AND  EXPERIMENTAL  POLLINATION. 


Excision. — The  results  of  the  experiments  with  the  various  types  of 
mutilation  are  presented  herewith.  Flowers  with  the  corolla  gone  closely 
resembled  old  flowers  with  the  petals  fallen  and  were  probably  mistaken  for 
them  (plate  17).  Tables  24  to  28  give  the  results  of  observations  in  which 
25  normal  flowers  and  5  flowers  of  each  kind  of  mutilation  were  used, 
with  the  exception  of  the  last,  in  which  the  numbers  were  equal.  The 
period  of  observation  was  one  hour  in  all  cases  but  the  second. 

Table  25. — Visitors  to  normal  and  mutilated  flowers. 


Species. 

Normal 
flowers. 

Petals 
removed. 

Petals 
shortened. 

Petals 
split. 

Stamens 

and 

style 

excised. 

Cotton 

over 
stamens. 

Cotton 

under 

stamens. 

Bombus  juxtus .... 
Prosopis  basalis. . . . 
Halictus  pulzenus. . 

Total 

23 

1 
0 

0 
0 
0 

12 
0 
0 

17 

2 
2 

17 

1 
1 

6 
0 
0 

7 
0 
0 

24 

0 

12 

21 

19 

6 

7:65 

Table  26. — Visitors  to  normal  and  mutilated  flowers. 


Species. 

Normal 
flowers. 

Petals 
shortened. 

Style  and 
stamens 
excised. 

6.6 
0:0 
5:6 
1:4 
1:1 
0:0 
0:0 

4:4 
1:1 
0:0 
0:0 
0:0 
0:0 
1:1 

2:5 

7:7 

4:10 

0:0 

2:3 

2:6 

0:0 

Total 

13:17 

6:6 

17:31 

Table  27. — Visitors  to  normal  and  mutilated  flowers. 

Species. 

Normal. 

Petals 
\i  width. 

Stamens 
removed. 

20 
15 
9 
8 
3 
7 
4 
6 
2 
2 
1 
2 
1 

7 
12 
2 
3 
0 
1 
5 
0 
0 
0 
1 
0 
1 

1 
3 
0 

0 
1 
0 
0 
0 
0 
0 
0 
0 

Total 

80 

32 

6:38 

GERANIUM    CAESPITOSUM. 
Table  28. — Visitors  to  normal  and  mutilated  flowers. 


43 


Species. 

Normal. 

Corolla    I              c, 
,      .        ,  |              Species, 
shortened.  | 

Normal. 

Corolla 
shortened. 

Apis  mellifica 

Bombus  juxtus 

occidentalis. . 
Prosopis  basalis 

elliptica.  .  .  . 
Megachile  wootoni. . . 
Andronious  sp 

16 
21 

8 
15 
13 
10 

2 

10 
9 
1 
15 
17 
10 
2 

Adrena  prunorum 

crataegi 

Osmia  melanotricha. . 
Halictus  pulzenus .... 
Anthophora  simillima. 

TotaJ 

1 
1 
3 

1 
3 

0 
0 
0 
2 
0 

94 

66 

In  all  cases  where  there  were  two  or  more  mutilations,  these  received 
relatively  twice  as  many  visitors  as  the  normal  flowers.  The  removal 
of  the  petals  practically  eliminated  visits,  while  shortening  them  decreased 
the  number  markedly.  The  excision  of  the  stamens,  or  of  these  and  the 
style,  led  to  the  greatest  increase  as  a  rule,  probably  because  of  the  exposure 
of  the  nectar.  The  use  of  cotton  to  mask  the  stamens  or  nectar  openings 
reduced  the  number  of  visitors  in  comparison  with  many  of  the  other 
mutilations,  but  not  below  that  for  the  normal  flowers. 

ARTIFICIAL  AND  PAINTED  FLOWERS. 

Crepe-paper  corollas. — The  corollas  were  replaced  by  crepe-paper  ones 
of  the  same  size  and  form  as  the  normal  and  of  the  colors  indicated  in 
table  29.  Four  of  each  color  or  a  total  of  20  crepe  corollas  were  used, 
together  with  4  flowers  with  normal  corollas. 

Table  29. — Visitors  to  normal  and  crepe-paper  flowers. 


Species. 

Normal. 

Red. 

Blue. 

Yellow. 

White. 

Green. 

34 
7 
4 
7 
4 
3 
2 
1 
1 
0 

1 
0 
0 
0 
0 
0 

1 

0 
0 

1 

6 
0 
0 
0 
0 
0 
1 
0 
0 

3 
0 
0 
0 
0 
0 
6 
0 
0 
5 

5 
0 
0 
1 
0 
0 
0 
0 
0 

1 

2 
0 
0 
0 
0 
0 
2 
0 
0 
0 

Halictus  pulzenus 

Monumetha  albifrons 

Syrphus  americanus 

Total 

63 

3 

9 

14 

7 

4:37 

In  spite  of  the  fact  that  the  table  shows  37  visits  to  artificial  flowers  to 
63  for  normal,  the  latter  were  only  one-fifth  as  numerous  and  hence  appear 
to  have  been  about  ten  times  as  attractive.  The  contrast  between  red  and 
green  on  the  one  hand  and  yellow,  blue,  and  white  on  the  other  suggests 
that  the  bees  were  influenced  in  some  degree  by  the  brightness  of  the  colors. 

ADDITION  OF  HONEY  AND  ODOR. 
Honey. — A  drop  of  honey  was  put  on  the  petals  of  half  of  the  flowers. 
Bombus  juxtus  landed  at  a  normal  flower  and  then  at  one  with  the  honey- 


44 


NORMAL  AND  EXPERIMENTAL  POLLINATION. 


drop  in  such  a  position  that  its  head  was  just  above  the  drop.  It  first 
walked  around  the  filament  column,  then  commenced  to  suck  honey  and 
continued  for  90  seconds,  until  the  drop  was  two-thirds  gone.  While 
sucking,  it  supported  itself  on  a  petal  with  the  front  and  hind  pairs  of  legs. 

Diluted  honey  was  placed  in  drops  at  the  base  of  the  filaments.  Halictus 
pulzenus  went  from  one  nectary  to  the  next,  sucking  nectar,  as  usual,  and 
did  not  notice  the  honej^.  Bombus  juxtus  came  and  crowded  Halictus 
away,  but  did  not  stay  long  enough  to  secure  all  the  honey.  At  the  next 
flower  there  was  a  drop  at  one  point  and  it  sucked  at  this  until  the  honey 
was  all  gone.  This  took  a  minute;  it  then  walked  around  the  flower  and 
dipped  its  ligule  into  each  nectary.  One  individual  stayed  at  a  honey  drop 
for  more  than  3  minutes.  After  this  it  walked  around  the  flower,  back  to 
the  honey-drop,  and  sipped  more  of  it.  The  end  of  the  ligule  did  not  reach 
the  nectary,  as  the  tip  was  visible  in  the  honey,  moving  in  all  directions. 
This  bee  flew  to  another  flower  that  had  a  drop  of  honey  in  a  similar  position 
and  walked  around  the  column  of  anthers  without  stopping  for  nectar. 

A  circle  of  diluted  honey  was  placed  around  the  base  of  the  filaments. 
Bombus  juxtus  took  a  few  sips  of  this,  but  did  not  stay  long.  Another 
juxtus  landed  with  its  head  pointed  toward  the  outside  of  the  flower  and 
sucked  honey  from  a  drop  that  had  run  half  way  down  the  petals.  It  then 
went  to  the  next  flower  which  had  honey  in  a  similar  position,  took  a  sip, 
and  flew  away.  When  Bombus  bifarius  came  to  a  flower  on  which  there 
was  diluted  honey,  it  stayed  and  sipped,  instead  of  trying  to  push  the  ligule 
into  the  nectaries.  However,  it  did  not  remain  until  all  the  honey  was 
gone,  but  flew  to  normal  flowers  and  took  nectar  there.  Halictus  pulzenus 
went  to  a  flower  with  a  honey-drop,  but  worked  at  all  the  nectaries  without 
finding  it. 

Diluted  honey  wab  put  around  the  base  of  the  stamens  of  10  flowers, 
which  were  placed  beside  10  normal  ones.  The  results  of  an  hour's  observa- 
tion are  shown  in  table  30. 

Table  30. — Visits  to  normal  and  honey  flowers. 


Species. 

Normal 
flowers. 

Honey 
flowers. 

13:101 
2:13 
2:2 
3:4 

10:12 
0:0 
0:0 
0:0 

juxtus 

Prosopis  varifrons 

Halictus  pulzenus 

Total 

20:120 

10:12 

While  there  were  one-half  as  many  visitors  to  the  honey  as  to  the  normal 
flowers,  these  averaged  but  one  visit  each  in  contrast  to  6  each  for  the 
normal.  In  addition,  7  bumble-bees  inspected  the  honey  flowers.  The 
effect  of  added  honey  in  disturbing  the  normal  response  is  well  shown  in  the 
case  of  Bombus  bifarius.  The  honey  flowers  received  nearly  as  many  visitors 
as  the  normal  ones,  but  practically  all  of  these  made  single  visits,  in  contrast 
to  an  average  of  8  for  the  normal  flowers. 


CHAMAENERIUM    ANGUST1F0LIUM.  45 

SUMMARY. 

Complete  inversion  of  the  flower  did  not  deter  bees  from  landing,  but 
it  did  prevent  their  finding  the  nectaries.  As  a  rule,  they  also  alighted  on 
flowers  with  the  nectaries  concealed  by  cotton,  but  Bombus  alone  succeeded 
in  finding  the  nectar.  The  total  number  of  visitors  to  the  mutilated  flowers 
was  twice  as  great  as  the  normal.  This  was  due  chiefly  to  the  greater 
attractiveness  of  the  flowers  with  stamens  excised,  since  the  removal  of 
the  petals  almost  completely  destroyed  the  attraction  and  shortening 
them  greatly  reduced  it.  Paper  flowers  received  a  considerable  number 
of  visitors,  but  they  were  only  about  a  tenth  as  attractive  as  the  normal 
ones.  The  effect  of  honey  on  the  flowers  was  to  reduce  the  number  of 
visitors  a  half  and  the  number  of  visits  six  times. 

CHAMAENERIUM  ANGUSTIFOLIUM. 
NORMAL  POLLINATION. 

Habit  and  structure. — These  plants  were  present  in  the  open  spaces 
along  Ruxton  and  Jack  Brooks,  where  the  communities  are  often  so  dense 
and  extensive  that  they  practically  crowd  out  all  other  species  where 
they  exist.  The  blooming  period  is  continuous  from  the  beginning  of  July 
until  the  first  of  September,  the  lower  flowers  on  the  stalk  maturing  first, 
and  then  as  the  stalk  elongates,  the  flowers  above  come  into  bloom.  The 
long  period  of  blooming  and  the  numerous  flowers  that  mature  at  any  one 
time  make  this  an  admirable  plant  for  study.  The  great  number  of  visitors 
always  present  on  bright  days  indicates  that  the  bees  find  it  a  very  desirable 
species.  Nectar  is  abundant  and  there  is  a  large  amount  of  pollen.  The 
pollen  grains  are  large  and  of  a  blue-green  color,  and  are  held  together  by 
the  sticky  threads  characteristic  of  the  Onagraceae. 

The  corollas  of  the  flowers  lie  in  a  more  or  less  vertical  plane  with  the 
style  recurved  and  its  branches  held  closely  together,  protecting  the  stig- 
matic  surfaces,  or  in  the  later  stage  with  the  style  projecting  in  front  of  the 
corolla  and  the  stigmatic  surfaces  exposed  on  the  outwardly  coiled  stylar 
branches.  The  stigmas  are  covered  with  blue-green  pollen  soon  after  they 
recurve.  A  large  number  of  seeds  develop,  indicating  that  the  method  of 
pollination  is  unusually  efficient.  The  petals  of  the  flowers  are  about  the 
size  of  the  Bombus  workers  and  so  form  a  very  convenient  landing- platform 
for  most  of  the  visitors  (plate  8). 

Behavior. — Bombus  juxtus  is  by  far  the  most  frequent  visitor,  although 
other  species  of  Bombus  and  Apis  are  abundant.  The  former  comes  for  nec- 
tar chiefly,  although  it  usually  collects  some  pollen  in  the  process,  while  a 
few  individuals  collect  pollen  alone.  Juxtus  lands  on  a  petal,  pushes  out 
its  proboscis,  and  finds  nectar  at  the  openings  between  the  bases  of  the  two 
upper  stamens.  While  sucking  nectar,  the  hind  legs  move  back  and  forth 
in  such  a  way  that  much  pollen  accumulates  in  the  corbiculae.  This  motion 
shakes  the  whole  flower,  and  pollen  from  anthers  and  from  the  hairs  covering 
the  bee's  body  falls  on  the  recurved  stigmatic  surfaces.  The  hairs  on  the 
dorsal  and  ventral  sides  of  Bombus  become  dusted  with  pollen.  One 
Bombus  juxtus  marked  with  white  paint  was  found  to  return  to  the  same 
group  of  flowers  a  number  of  times  each  hour,  as  well  as  day  after  day. 


46  NORMAL  AND  EXPERIMENTAL  POLLINATION. 

It  followed  the  same  route  each  time  among  the  flowers.  The  capacity  to 
visit  many  flowers  in  succession  varies  in  the  different  species.  B.  juxtus 
visited  an  average  of  36  flowers  in  succession,  while  proximus  came  to  an 
average  of  17.  One  individual  of  juxtus  visited  116  flowers  in  one  circuit, 
and  other  individuals  went  respectively  to  95,  62,  and  52  flowers. 

The  queen  of  Bombus  proximus  lands  and  takes  nectar,  but  it  is  so  large 
that  the  under  tip  of  the  abdomen  rubs  the  style  branches  and  in  that  way 
leaves  pollen  on  them.  Much  of  the  pollination  is  done,  however,  when  the 
stamens  are  shaken.  This  queen  goes  from  flower  to  flower  for  nectar 
without  making  any  effort  to  get  pollen.  The  drone  of  this  species  poises 
in  the  air  and  then  lands  on  the  stamens;  it  takes  no  nectar,  but  collects 
pollen  alone.  It  scrapes  this  off  with  the  second  pair  of  legs  and  from  these 
on  to  the  third  pair,  where  a  heavy  load  of  pollen  soon  accumulates.  When 
poised  in  the  air  in  front  of  the  flowers,  it  is  scraping  pollen  from  the  sides  of 
its  abdomen  and  putting  it  in  the  corbiculae.  It  works  very  nervously 
and  rapidly  at  each  flower,  but  flies  deliberately  from  one  to  another. 

Bombus  bifarius,  upon  landing  at  a  flower,  takes  a  position  in  which  the 
tip  of  the  abdomen  is  between  the  style  and  the  petals.  It  comes  for  nectar 
only  and  seldom  touches  the  recurved  styles  because  of  the  position  of  the 
abdomen.  Apis  mellifica  lands  below  and  then  has  to  crawl  to  the  opening 
of  the  nectary.  It  comes  for  both  pollen  and  nectar,  depending  upon  its 
needs  at  the  time.  Megachile  pugnata,  although  a  much  less  frequent  visitor 
to  these  flowers,  is  a  very  effective  pollinator.  Its  fewer  visits  are  doubtless 
due  to  the  fact  that  this  species  is  not  so  common  in  this  locality.  The 
abdominal  brushes  are  large  and  yellow  and  consist  of  unusually  long,  stiff 
bristles.  It  lands  in  the  proper  place  for  sucking  nectar  and  straddles  the 
style.  This  places  the  mouth-parts  directly  above  the  opening  to  the  necta- 
ries. It  pushes  out  its  proboscis  and  sucks  nectar,  while  the  hind  legs  move 
rapidly  and  scrape  pollen  on  to  the  abdominal  brushes.  Halictus  (Lasioglos- 
sum)  sp.  hangs  on  to  the  anthers  with  its  front  legs  in  some  flowers,  but 
usually  twists  its  abdomen  around  the  base  of  the  filaments  while  sucking 
nectar.  This  places  it  in  a  position  to  have  pollen  fall  on  it,  and  as  the  bee 
flies  away,  pollen  is  jarred  loose  and  falls  on  the  stigmatic  surface  of  the 
flower.  The  brushes  on  the  legs  collect  pollen  as  when  it  hangs  on  the 
stamens.  Vespa  germanica  stands  on  the  petals,  reaches  in  to  the  nectary, 
and  sucks  nectar.  While  sipping,  Andrena  madronitens  elevates  the  tip 
of  its  abdomen  in  such  a  way  that  the  scopa  rubs  the  style  branches  in  some 
flowers  and  the  anthers  in  others.  This  makes  it  a  very  effective  pollinator 
and  one  that  uses  the  scopa  in  a  different  manner  from  other  bees.  There 
are  also  long  blue-green  pollen  loads  on  its  legs.  Argynnis  atlantis  comes 
for  nectar,  the  tip  of  its  abdomen  rubbing  the  recurved  stigmas  as  it  works. 

The  normal  visitors  to  Chamaenerium  are  given  in  tables  31  to  33.  In 
the  first  case,  120  flowers  on  20  racemes  were  observed  for  30  minutes,  in 
the  second  80  flowers  on  12  racemes  for  an  hour,  and  in  the  third  140  flowers 
on  25  racemes  for  two  successive  hour  periods. 

For  an  hour  period  the  number  of  visitors  varied  from  28  to  4,  and  the 
number  of  visits  from  158  to  728,  the  average  number  of  visits  per  insect 
ranging  from  6  to  50.  Bombus  contributed  45  of  the  total  of  60  visitors, 
and  these  made  1,391  of  the  1,424  visits.     A  calendar  of  the  normal  visitors 


CHAMAENERIUM   ANGUSTIFOLIUM. 
Table  31. — Visitors  and  visits  to  normal  flowers. 


47 


Species. 

Visitors. 

Visits.     I              Species. 

Visitors. 

Visits. 

Bom  bus  juxtus 

bifarius 

appositus.  .  . 

Megachile  wootoni . . . 

pugnata. .  . 

Prose-pis  basalis 

Monumetha  albifrons. 
Syrphus  americanus . . 

Total 

4 
1 
1 
2 
1 
3 
1 
1 

56         |  Megachile  wootoni. . . 
3            Prosopis  elliptica.  .  .  . 
1            Syrphus  americanus. . 

2 
2 

1 

9 
2 
1 

3 
4 
3 
1 

Total 

21 

413 

Bombus  juxtus 

bifarius 

proximus.  .  . 
Syrphus  americanus. . 
Thanaos  martialis .  .  . 

Total 

9  to  10 
a.  m. 

12:586 
1:27 
6:113 
1:1 
1:1 

10  to  11 
a.  m. 
2:173 
0:0 
2:31 
0:0 
0:0 

14 

79 

Bombus  juxtus 

bifarius 

proximus. . . . 

6 
6 
4 

163 
124 
114 

21:728 

4:204 

to  Chamaenerium  during  a  half-hour  period  is  given  below,  9  stalks  bearing 
85  open  flowers  being  observed. 

Calendar  1. — Visits  to  normal  flowers. 

8h58m  Apis  mellifica  3. 

9  00     Megachile  relativa  8. 

9  02     Bombus  juxtus  20. 

9  06     Megachile  vidua  6. 

9  08  Megachile  texana  15;  Bombus  occiden- 
tals 11. 

9  09  Megachile  texana  3;  relativa  16; 
wootoni  10. 


9hllm  Apis  mellifica  4;  Bombus  occidentalis  15. 

9  13     Apis  mellifica  3. 

9  15     Bombus  juxtus  3 ;  hunti  5. 

9  17     Bombus  juxtus  18;  Selasphorus  platy- 

cercus  7;  Apis  mellifica  5. 
9  18     Apis  mellifica  4;  Bombus  hunti  6. 
9  35     Bombus  bifarius  11. 


A  summary  of  the  above  visitors  is  given  in  table  32. 
Table  32. — Visitors  to  normal  flowers. 


Species. 

Visitors  and 
visits. 

Species. 

Visitors  and 
visits. 

5:19 
3:41 

2:24 
2:18 
2:16 
1:6 

1:7 

occidentalis 

2:26 
2:11 
1:11 

Selasphorus  platycercus 

Total 

21:179 

All  the  individuals  of  Bombus  working  on  one  group  of  flowers  during  an 
hour  were  collected,  with  the  results  given  in  table  33. 

Table  33. 


Species. 

Workers. 

Drones. 

4 
11 

6 
32 

Total 

15 

38 

48 


NORMAL  AND  EXPERIMENTAL  POLLINATION. 


These  results  show  that  the  drones  of  some  species  of  Bombus  gather 
nectar,  while  among  the  honey-bees  this  is  not  the  case. 

Merritt  (1897:4)  found  the  floral  structure  as  described  by  Mueller 
(1883:261),  except  that  she  noted  no  lengthening  of  the  style  as  the  flower 
expanded.  The  style  seemed  unduly  long,  to  such  an  extent  that  the  lobes 
were  often  so  high  that  the  bee  missed  them.  Only  1  honey-bee  in  5  touched 
a  stigma.  Honey-bees  and  Osmia  californica  were  the  chief  visitors. 
Knuth  (1906:441)  records  a  number  of  variations  in  the  flower  mechanism, 
and  gives  lists  that  show  this  to  be  primarily  an  apid  flower. 

EXPERIMENTS. 

CHANGE  OF  POSITION. 

Racemes  inverted. — When  the  flower-stalk  of  Chamaenerium  is  in- 
verted, the  parts  are  reversed  with  respect  to  the  position  in  which  the 
bee  is  accustomed  to  find  them.  The  style  and  the  stamens  now  project 
upward,  leaving  only  the  petals  and  sepals  of  the  lower  half  of  the  flower 
as  a  place  to  land.  These  often  project  backward  in  a  such  a  way  that  it  is 
difficult  for  an  insect  to  stay  on  them.  Three  individuals  of  Bombus  juxtus 
went  to  inverted  flowers  at  different  times  and  tried  to  discover  the  nectar, 
but  flew  away  without  finding  it.  In  another  experiment  wet  cotton  was 
tied  over  the  cut  end  of  three  racemes  to  keep  the  flowers  from  wilting,  and 
each  one  inverted  was  fastened  alongside  a  normal  cluster.  Table  34 
gives  the  results  of  an  hour's  observation  on  two  different  days,  an  equal 
number  of  normal  and  inverted  flowers  being  used  in  each  case. 

Table  34. — Visitors  and  visits  to  normal  and  inverted  racemes. 


Species. 

Experiment  1. 

Experiment  2. 

Normal. 

Inverted. 

Normal. 

Nectar 
found. 

Nectar 
not  found. 

Inverted. 

Horizontal. 

Bombus  juxtus 

proximus.  .  . 
Halictus  pulzenus.. .  . 

6:33 

0:0 

2:1 

3:8 
1:2 

0:0 

3:8 
0:0 
0:0 

3:8 
0:0 
0:0 

6:30 
0:0 

0:0 

8:48 

1:1 

0:0 

Total 

8:34 

4:10                3:8 

3:8 

6:30 

9:49 

In  the  first  experiment  as  many  individuals  of  Bombus  juxtus  visited 

inverted  as  normal  stalks,  but  the  number  of  flowers  visited  was  only  half  as 

great.     In  the  second,  the  visitors  to  the  changed  clusters  were  four  times 

as  numerous  and  the  number  of  flowers  visited  almost  10  times  as  great. 

However,  this  was  due  largely  to  the  presence  of  the  horizontal  racemes, 

the  visitors  and  visits  to  the  inverted  ones  being  much  the  same  for  the 

two  cases. 

MUTILATION. 

Floral  envelopes  removed. — This  mutilation  makes  the  whole  raceme 
much  less  conspicuous  even  than  when  in  bud,  and  gives  it  a  pale,  feathery 
appearance  not  at  all  like  the  normal  one.  The  24  mutilated  stalks  were 
4  feet  away  from  those  bearing  normal  flowers  (plate  17). 


CHAMAENERIUM   ANGUSTIFOLIUM. 
Table  35. — Visitors  to  flowers  with  floral  envelopes  removed. 


49 


Species. 

Visitors. 

11:136 
1:1 
1:1 

1:1 

Total 

15:140 

Bombus  juxtus  readily  distinguished  between  buds  and  these  mutilated 
flowers,  for  it  never  stopped  at  the  former. 

Upper  petals  and  the  included  sepal  removed. — This  sepal  is  just 
behind  the  opening  to  the  nectary  and  looks  as  if  it  might  be  a  guide  to 
it.  Bombus  juxtus  went  to  flowers  with  these  parts  removed  and  to  normal 
flowers  indiscriminately,  just  as  they  happened  to  be  in  its  path. 

Stamens  and  style  removed. — Bombus  juxtus  visited  flowers  with 
these  parts  removed  and  found  the  nectar  at  once.  It  went  to  three 
flowers  in  succession,  but  had  some  difficulty  hanging  on. 

The  following  notes  made  during  5  minutes  of  observation  indicate  that 
Bombus  juxtus  took  little  notice  of  all  the  above  changes.  An  equal  number 
of  normal  and  mutilated  flowers  were  under  observation. 


10h20m  Bombus  juxtus  flew  over  flowers  with 
the  corolla  removed,  but  stopped 
at  2  with  the  stamens  alone  gone. 
A  second  one  stopped  at  2 
flowers  with  the  petals  gone  and 
at  3  normal  ones. 

10  21     B.  juxtus,  2  flowers  with  stamens  gone. 


10h22m  B.  bifarius,  3  flowers  with  the  upper 
3  petals  gone  and  3  normal. 

10  23  B.  juxtus,  4  normal  and  then  2  flowers 
with  the  upper  petals  gone. 

10  24  B.  juxtus,  3  flowers  with  the  upper 
petals  gone  and  2  normal. 

10  25     B.  juxtus,  5  normal. 


The  relative  numbers  of  visits  made  by  the  various  species  of  bees  to  the 
different  kinds  of  mutilated  flowers,  as  well  as  to  the  normal  ones,  are  shown 
in  table  36.  On  July  17  and  18,  10  normal  flowers  and  5  mutilated  ones  of 
each  type  were  used,  one  or  more  of  each  being  placed  in  each  raceme;  the 
time  of  observation  was  1  hour.  For  the  next  two  periods  of  an  hour  and 
a  half  each,  4  flowers  of  one  kind  were  arranged  on  each  stalk. 

The  results  obtained  in  this  experiment  relate  chiefly  to  the  behavior 
of  Bombus,  as  the  other  4  genera  made  but  17  of  the  210  visits  recorded. 
Of  the  193  visits  by  bumble-  bees,  B.  juxtus  made  173  and  B.  bifarius  but 
20.  The  actual  number  of  visits  to  normal  and  mutilated  flowers  is  nearly 
equal,  but  the  normal  flowers  were  a  third  as  numerous  and  hence  about 
twice  as  attractive.  However,  the  contrast  between  the  different  types  of 
mutilated  flowers  is  so  sharp  as  to  indicate  an  intentional  selection.  Thus, 
flowers  with  the  perianth,  stamens,  and  styles  removed  received  but  6 
visits  out  of  a  total  of  114  for  mutilated  flowers,  while  those  with  either 
stamens  or  styles  excised  obtained  less  than  half  as  many  as  those  with 
petals  or  both  sepals  and  petals  removed.  On  the  other  hand,  the  visits 
to  both  the  latter  were  a  third  less  tnan  to  the  flowers  with  the  stamens  and 
styles  excised  but  the  perianth  intact.     While  the  results  are  not  entirely 


50 


NORMAL  AND  EXPERIMENTAL  POLLINATION. 


in  accord,  it  is  significant  that  166  visits  were  made  to  flowers  with  corollas 
in  contrast  to  44  to  those  without. 


Table  36. — Visits  to  normal  and  mutilated  flowers. 

Time. 

Species. 

Normal. 

Petals 
off. 

Sepals 
and 

petals 
off. 

Stamens 
excised. 

Styles 
excised. 

Stamens 

and  styles 

excised. 

Perianth, 

stamens, 

and  styles 

off. 

July  17 
July  18 

July  21 
July  25 

13 
55 

1 
0               12 
12                 0 

1 
7 

7 
0 

12 
17 

0 
0 

Do 

Total 

68       |       12              12       j         8                  7                29 

0:68 

2 
4 
1 

0 
0 
0 

2 

1 
0 

0 
1 
0 

0 
0 
0 

2 
3 
0 

3 
0 
0 

Monumetha  albifrons .  .  . 
Megachile  wootoni 

Total 

Bombus  juxtus 

bif  arius 

Andrena  madronitens .  .  . 
Halictus  pulzenus 

7       |         0       |         3                1 

0                  5 

3:12 

18 
1 
0 
2 

5 

1 
1 

3 
0 
0 
0 

0 
0 
0 
0 

0 
0 
0 
0 

2 
15 

2 

0 
3 
0 
0 

Total 

Grand  total 

21       |         8      |.      3       |        0        |        0               20 

3:34 

96       j       20       1        18       !         9         j         7                54 

1 

6:114 

In  the  following  experiments  one  raceme  was  left  normal  and  one  mutilated 
by  each  of  the  various  types  of  excision.  In  the  tables  the  first  number 
in  each  column  represents  the  number  of  visitors,  the  second  the  number 
of  flowers  visited.  The  first  observations  were  made  on  July  19  from 
9h05m  to  10h05m  a.m.  and  the  second  on  the  same  date  from  10h05m  to 
12h05m  a.m. 

Table  37. — Visits  to  normal  and  mutilated  flowers. 


Species. 

"3 

g 
o 

B  T3 

Petals 

and 

sepals 

excised. 

l] 

S  "2 

Stamens 

and 

styles 

excised. 

Ovary 
alone 
left. 

Bombus  juxtus 

proximus 

Megachile  wootoni .... 

Total 

43:157 
3:6 
2:3 

20:89 
0:0 
0:0 

22:99 
0:0 
1:2 

40:165 
2:12 
0:0 

49:143 
4:10 
0:0 

38:132 
1:2 
0:0 

212:785 
10:30 
3:5 

48:166 

20:89 

23:101 

42:177 

53:153 

39:134 

225:820 

Bombus  juxtus 

proximus 

Megachile  wootoni .... 
Monumetha  albifrons. . 

Total 

27:179 
3:18 
2:8 
1:3 

14:211 
1:2 
0:0 
0:0 

33:208 

15:213 

Bees  flying  to  the  community  usually  alighted  upon  flowers  with  corol- 
las.    Once  landed,   they  passed  on  to  the  flowers  in  order,   with  little 


CHAMAENERIUM   ANGUSTIFOLIUM. 


51 


regard  to  the  type  of  mutilation.  It  is  significant  that  the  removal  of  the 
petals  or  the  perianth  reduced  the  number  of  visitors  more  than  half  in 
every  case,  and  with  a  single  exception  had  a  somewhat  similar  effect 
upon  visits.  The  flowers  with  stamens  or  styles  or  both  excised  were  treated 
essentially  as  normal  ones,  but  those  with  ovary  and  nectary  alone  left 
received  practically  five  times  as  many  visitors  and  visits,  probably  owing 
to  the  greater  fragrance  and  accessibility  of  the  nectar. 

ARTIFICIAL  AND  PAINTED  FLOWERS. 
Crepe-paper  corollas. —  Red,  blue,  green,  white,  or  yellow  corollas 
were  made  to  simulate  and  replace  the  normal  ones,  leaving  the  stamens 
and  style  intact.  No  bees  went  to  the  flowers  with  crepe  corollas,  not 
even  to  those  in  which  a  drop  of  honey  was  placed  on  the  nectary.  At 
another  trial  of  crepe  corollas  no  visitors  were  attracted  until  a  drop  of 
diluted  honey  was  put  on  the  nectary,  and  even  then  but  one  bee,  Bombus 
juxtus,  came  to  the  flowers  for  a  chance  visit.  In  another  experiment, 
half  of  the  flowers  on  the  raceme  were  left  normal  and  paper  corollas  were 
alternated,  as  it  was  thought  that  the  habit  of  going  from  one  flower  to 
the  next  would  cause  some  of  the  bees  to  stop  at  those  with  artificial  corollas. 
In  spite  of  this,  not  one  bee  stopped  at  a  flower  with  crepe  corolla,  although 
they  flew  low  to  inspect  them. 

Painted  corollas. — Natural  corollas  were  painted  with  water-colors 
on  the  upper  side.  While  the  texture  of  the  petal  is  such  that  the  colors 
do  not  spread  uniformly  over  the  surface,  they  show  up  very  well.  Table  38 
gives  the  results  of  these  experiments,  5  flowers  of  each  color  and  10  normal 
ones  being  used  in  each  case.  The  first  observations  were  made  on  July  21 
from  8  to  10  a.  m.  and  the  second  on  the  following  day  from  9  to  10  a.  m. 

Table  38. — Visits  to  normal  and  painted  flowers. 


Species. 

Normal.         Red. 

White. 

Yellow. 

Green. 

Blue. 

51 
0 
0 
0 

10 
0 
0 
0 

10 
1 
1 
1 

10 
0 
0 
0 

16 
0 
0 
0 

10:56 
0 
0 
0 

Syrphus  americanus 

Thanaos  martialis 

Total 

51 

10 

13 

10 

16 

10:59 

48 
3 

1 
0 
0 

10 
0 
0 
0 
0 

6 
0 
0 
0 
0 

6 
2 
0 

1 

7 
0 
0 
0 
0 

19:48 
0 
0 
0 
0 

Megachile  wootoni 

Monumetha  albifrons 

Syrphus  americanus 

Total 

52 

10 

6 

10 

7 

19:52 

103 

20 

19 

20 

While  there  were  a  few  more  visits  to  the  painted  than  to  the  normal 
flowers,  the  former  were  2.5  times  more  numerous  and  the  actual  ratio  of 
normal  to  painted  is  103:44.  Bombus  juxtus  made  203  of  the  total  of  214 
visits  to  all  kinds  of  flowers.     It  showed  no  pronounced  color  preference, 


52 


NORMAL  AND  EXPERIMENTAL  POLLINATION. 


though  blue  led  with  29  visits,  followed  by  green  23,  red  20,  white  and  yellow 
16  each.  Oddly  enough,  white  and  yellow  were  the  only  colors  sought  by 
the  other  species,  but  the  numbers  are  too  small  to  be  significant.  The 
behavior  of  one  Bombus  juxtus  was  noted  as  it  worked  from  flower  to  flower 
and  the  following  course  was  observed:  blue,  normal,  hovered  over  green, 
normal;  next  stalk,  blue;  third  stalk,  blue,  normal,  blue,  normal. 

ADDITION  OF  NECTAR  AND  ODOR. 

Honey. — When  a  drop  of  honey  was  placed  at  the  opening  to  the  nectary 
in  a  group  of  normal  flowers,  Apis  mellifica  found  it  at  once  and  stayed  at 
the  flower  6  minutes.  In  another  experiment,  honey  was  placed  on  every 
flower  on  one  plant,  but  the  number  of  visitors  was  no  more  numerous  than 
to  the  normal  plants  adjoining.  The  bees  merely  happened  to  visit  it  and 
were  not  especially  attracted  by  the  honey.  However,  when  Bombus 
juxtus  did  find  the  latter,  it  stayed  at  the  drop  until  this  was  consumed. 
When  the  drop  of  honey  was  put  on  the  style  branches,  Bombus  sucked 
it  up  as  readily  as  when  it  was  over  the  openings  to  the  nectaries. 

Odor. — Flower  perfumes  were  put  on  cotton-wads  and  these  then 
wound  around  the  several  pedicels  under  the  calyx.  The  groups  of  flowers 
on  which  the  different  odors  were  placed  were  arranged  with  respect  to  the 
direction  of  the  wind  so  as  to  make  the  odor  in  each  case  as  distinctive  as 
possible.  Twelve  flowers  of  each  odor  were  used  in  addition  to  24  normal 
ones.  The  two  sets  of  observations  were  made  during  succeeding  hours  on 
August  9. 

Table  39. — Visitors  and  visits  to  perfumed  flowers. 


Species. 

Normal. 

Violet 
perfume. 

Carnation 
perfume. 

Crab-apple 
perfume. 

8:75 
7:51 
4:40 
1:3 

7:26 
3:10 
4:18 
0:0 

1:3 

1:5 
1:3 

0:0 

Total 

20:169 

14:54 

3:11 

15:111 
11:52 

9:86 

0:0 

5:30 
2:3 
0:0 
0:0 

16:71 
8:29 
4:14 
1:2 

1:2 
9:24 
1:1 
0:0 

Total 

35:249 

7:33 

29:116 

11:27 

55:418 

21:87 

32:127 

11:27 

The  flowers  with  carnation  were  shaded  more  than  those  with  violet  in 
the  first  part  of  the  experiment,  which  probably  accounts  for  the  few  visits. 
During  the  next  hour  of  observation,  carnation  was  in  a  different  location 
and  many  more  visitors  came  to  it.  The  number  of  visitors  per  flower  was 
practically  the  same  for  normal  and  for  perfumed  stalks,  but  these  averaged 
only  4  visits  each  to  the  perfumed  flowers  in  contrast  to  8  each  for  the 
normal  ones,  indicating  again  something  of  the  usual  disturbance  caused 
by  strange  odors. 


CHAMAENERIUM   ANGUSTIFOLIUM. 


53 


Perfumes. — Either  "Love  me,"  "Three  flowers,"  "Poudre  azure,"  or 
camphor-ball  powder  was  sprinkled  over  the  nectaries  on  half  of  the  flowers 
on  each  of  four  stalks.  Bombus  juxtus  was  the  only  visitor  during  the 
hour  of  observation  (table  40). 

Table  40. — Visits  of  Bombus  juxtus  to  scented  flowers. 


Scented  powder. 

Normal. 

Scented. 

Inspections 
of  scented. 

6:9 
2:6 
1:3 
0:0 

1:2 
0:0 
0:0 
0:0 

4:6 
3:8 
1:1 
1:1 

Total 

8:18 

1:2 

9:16 

The  difference  in  behavior  as  compared  with  that  shown  in  table  39  is 
probably  to  be  explained  by  the  fact  that  the  appearance  of  the  flower  was 
visibly  changed  by  the  powder.  This  also  seems  to  furnish  the  reason  for 
the  large  number  of  inspections  indicated  in  the  last  column. 

Flavoring  extracts. — Extract  of  vanilla,  lemon,  almond,  or  peppermint 
was  poured  on  absorbent  cotton  and  a  small  wad  wrapped  around  the  ovary 
under  the  calyx.  This  changed  the  odor  of  the  flower,  but  did  not  affect 
its  appearance.  Visitors  to  normal  flowers  were  recorded  only  for  the  first 
experiment.     All  the  observations  were  made  on  August  8,  the  first  two 

Table  41. — Visitors  and  visits  to  flowers  scented  with  extracts. 


Species. 

Normal. 

Vanilla. 

Peppermint. 

Lemon. 

Almond. 

9:30 

7:18 
1:2 

1:5 
0:0 
1:1 

5:20 

1:5 

1:1 

3:12 
3:12 
1:1 

3:10 

0:0 

1:1 

Total 

17:50 

2:6 

7:26 

7:25 

4:11 

1:2 
0:0 
1:1 

1:2 
0:0 
0:0 

0:0 
0:0 
0:0 

4:9 
2:4 
2:3 

Total 

2:3 

1:2 

0:0 

8:16 

3:7 

2:5 
0:0 

0:0 
0:0 
1:1 

1:2 
0:0 
0:0 

8:10 
9:10 
1:2 

Total 

5:12 

1:1 

1:2 

18:22 

2:3 
0:0 
0:0 

1:2 
2:4 
3:7 

0:0 
0:0 
0:0 

1:2 
0:0, 
6:6 

Total 

2:3 

6:13 

0:0 

7:8 

11:24 

15:42 

8:27 

37:57 

54  NORMAL  AND  EXPERIMENTAL  POLLINATION. 

for  hour  periods  from  9h35m  to  llh35m  in  the  morning  and  the  next  two  for 
an  hour  period  from  2  to  4  in  the  afternoon. 

Both  visitors  and  visits  were  slightly  though  not  significantly  greater 
to  the  scented  flowers.  The  grand  totals  for  the  different  odors  are  much 
alike,  except  in  the  case  of  almond.  While  visited  least  in  the  first  experi- 
ment, its  total  was  2  to  4  times  greater  than  for  the  others. 

SUMMARY. 

The  inversion  of  the  flower  resulted  in  about  half  of  the  visits  being 
fruitless  at  first,  but  later  both  inverted  and  horizontal  flowers  received 
many  more  visits  than  the  normal.  Mutilated  flowers  in  general  were  about 
half  as  attractive  as  normal  ones,  but  they  differed  greatly  among  them- 
selves. The  removal  of  the  corolla  reduced  visits  from  a  half  to  a  fourth, 
in  spite  of  the  marked  habit  of  Bombus  in  visiting  Chamaenerium  flowers 
in  order  from  the  bottom  upwards.  On  the  other  hand  the  removal  of  all 
flower  parts  except  the  ovary  and  the  nectary  increased  the  visits  5  times 
over  the  normal,  doubtless  because  the  nectar  was  more  fragrant  and 
accessible,  thus  permitting  the  bees  to  work  more  rapidly.  Artificial 
flowers  of  paper  were  often  inspected,  but  they  received  only  a  single  visit, 
in  spite  of  the  addition  of  honey.  Painted  ones  were  about  half  as  attractive 
as  normal  flowers,  suggesting  that  the  neglect  of  artificial  flowers  was  due  to 
small  differences  in  form  and  texture,  since  the  colors  were  unnatural  in 
both  cases.  Blue  was  the  preferred  color,  but  not  decisively  so.  Honey 
did  not  attract  greater  numbers  of  bees,  while  scented  powders  almost 
eliminated  visits,  the  number  of  inspections  equaling  the  visits  to  normal 
flowers.  The  number  of  visitors  was  the  same  for  blossoms  perfumed  with 
other  flower  odors  and  normal  ones,  but  the  visits  were  about  half  as  many 
to  the  former.  Flavoring  extracts  seemed  to  increase  attraction  slightly, 
but  the  significant  fact  was  the  marked  effect  of  almond  in  augmenting  the 
number  of  visitors. 

PACHYLOPHUS  CAESPITOSUS. 

NORMAL  POLLINATION. 

Habit  and  structure. — This  species  possesses  the  largest  and  most 
fragrant  flowers  of  any  in  the  region.  It  is  white  in  color  the  first  evening, 
becoming  pink  the  next  morning.  When  the  calyx 
is  normal,  the  flowers  open  between  5  and  7  in  the 
evening  and  the  process  usually  requires  but  2  to  7 
minutes,  the  unfolding  of  the  petals  being  so  rapid 
that  the  movement  is  easily  seen.  The  style  and 
stamens  are  covered  with  very  small  black  diptera 
when  the  flower  opens.  At  this  time  the  anthers  are 
dehiscing  and  the  stigmas  are  receptive.  The  under 
surface  of  the  stigma  lobes  is  covered  with  pollen,  but 
the  receptive  surface  is  free  from  it.  The  tube  of 
the  calyx  is  about  10  cm.  long  and  is  filled  with  nectar 
for  more  than  half  its  length  at  the  time  of  opening 
(plate  9).  The  amount  of  nectar  varies  considerably, 
as  is  shown  by  its  weight  in  several  flowers.     These  were  picked  at  7 


Weight  of 

nectar. 

gm. 

1 

0.0135 

2 

.0430 

3 

.0065 

4 

.0280 

5 

.0475 

6 
Av 

.0355 

.0290 

PACHYLOPHUS   CAESPITOSUS.  55 

o'clock  in  the  evening  just  after  opening,  but  before  visitors  were  ob- 
served. The  absence  of  pollen  on  the  stigmas  furnished  additional  evidence 
that  they  had  not  been  visited.  The  nectar  was  blown  out  of  the  tube  on 
a  glass  slide  and  weighed  immediately. 

Robertson  (1892:272)  has  given  a  list  of  visitors  to  Oenothera  biennis 
and  0.  fruticosa,  and  described  the  structure  of  the  latter.  The  stigma 
exceeds  the  anthers  and  is  inclined  to  the  lower  side  so  that  it  strikes  the 
ventral  surface  of  visiting  bumble-bees.  The  tube  measures  14  to  20  mm. 
and  can  be  drained  only  by  the  largest  bees,  though  shorter-tongued  ones 
can  reach  a  little  of  the  nectar  when  the  tube  is  fullest.  Hitchcock  (1893: 
362)  has  observed  that  the  stigma  in  Oenothera  missouriensis  may  protrude 
from  the  bud  as  early  as  2  p.  m.,  though  the  flower  opens  fully  only  during 
the  latter  part  of  the  afternoon.  The  narrow  calyx-tube,  about  11  cm. 
long,  is  often  half  filled  with  nectar.  With  the  exception  of  ants,  the 
only  visitor  was  a  sphinx-moth,  Celerio  lineata,  which  came  in  abundance 
just  before  8  p.  m.,  but  ceased  its  visits  at  dark.  The  insect  pushed  its 
head  into  the  throat  as  far  as  possible,  but  was  able  to  reach  only  the  upper 
portion  of  the  nectar,  and  was  caught  in  the  flower  by  its  endeavor  to  secure 
more.  Merritt  (1897:4)  has  noted  that  the  flowers  of  0.  biennis  open 
about  6  p.  m.  and  close  about  9  a.  m.  While  the  stigmas  are  2  to  6  mm. 
beyond  the  anthers,  a  slight  breeze  is  sufficient  to  bring  them  into  contact. 
By  7h30m  p.  m.  pollen  was  found  on  nearly  all  the  stigmas,  though  no  night 
moths  were  seen.  The  odor  is  faint,  but  the  large,  pale  flowers  are  con- 
spicuous at  night.  In  0.  californica  the  flowers  at  6,000  feet  are  always 
fully  open  by  5  p.  m.  and  remain  conspicuous  and  fragrant  throughout 
the  night.  Honey-bees  collect  pollen  as  soon  as  the  flowers  open  and 
usually  strike  the  stigmas  first,  since  the  latter  slightly  exceed  the  anthers. 
Nectar  is  not  abundant  at  night,  but  by  morning  it  is  sometimes  an  inch 
deep  in  the  tube;  the  stigmas  are  visibly  pollinated  and  the  pollen  is  gone 
from  the  anthers.  Longyear  (1909: 105)  has  described  the  opening  of  the 
flower  and  its  pollination  in  Oenothera  pinnatifida. 

Behavior. — Three  species  of  large  hawk-moths  come  to  the  flowers 
very  soon  after  they  open  each  night,  namely,  Protoparce  quinquemaculata, 
Hyloicus  separatus,  and  Celerio  lineata.  The  first  two  have  a  proboscis 
9.5  to  10.5  cm.  long,  which  enables  them  to  reach  to  the  bottom  of  the  deepest 
tube.  It  was  found  that  each  moth  stays  at  a  newly  opened  flower  until 
it  obtains  all  the  nectar  that  it  can  reach.  Protoparce  worked  as  long  as 
38  seconds  at  such  flowers,  but  only  3  to  10  seconds  at  those  that  had  been 
previously  visited.  Celerio  has  a  much  shorter  proboscis,  about  4.5  cm. 
long,  and  is  limited  to  the  nectar-supply  in  the  upper  half  of  the  tube. 
These  moths  fly  swiftly  through  the  air  to  a  group  of  evening  primroses, 
when  they  stop  over  them,  unroll  the  proboscis  and  hover  in  this  position, 
gradually  descending  until  the  tip  of  the  ligule  is  above  the  opening  to  the 
tube.  After  a  few  trials,  the  proboscis  is  gradually  pushed  down  the  tube 
Until  it  reaches  the  nectar,  after  which  it  moves  downward  slowly  as  the 
nectar  is  sipped  up.  When  it  has  exhausted  the  nectar,  the  moth  rises  above 
the  flower  and  passes  to  the  next.  While  poised  in  the  air  above  the 
flower  after  a  visit,  its  proboscis  is  covered  with  large  masses  of  pollen 
and  viscin  threads  at  the  point  of  contact  with  the  anthers.     When  it  dips 


56 


NORMAL  AND  EXPERIMENTAL  POLLINATION. 


into  the  next  flower,  these  usually  come  in  contact  with  the  stigmatic 
surface,  which  acquires  more  and  more  pollen  with  each  visit.  The  hawk- 
moths  continue  to  come  for  an  hour  or  so  after  dark,  and  perhaps  later  if 
nectar  is  still  available.  They  are  not  frightened  by  lights  being  thrown 
on  them  and  in  consequence  their  movements  can  be  readily  followed  by 
means  of  a  flashlight. 

EXPERIMENTS. 
ARTIFICIAL  FLOWERS. 

Crepe-paper  flowers. — Artificial  flowers  were  made  of  crepe-paper 
and  provided  with  calyx-tubes  of  glass.  Some  of  these  were  coated  with 
paraffin  to  stiffen  them  and  others  were  shaped  by  stretching  the  paper. 
The  calyx-tube  was  filled  with  a  sirup  made  of  beet-sugar,  and  a  drop  of 
nectar  drawn  from  a  flower  placed  at  the  top.  The  calyx-tubes  of  natural 
flowers  from  which  the  nectar  had  been  taken  were  then  filled  to  the  top 
with  sugar  solution.  In  no  case  were  the  crepe-paper  flowers  visited  or 
even  inspected,  a  fact  difficult  to  explain,  since  the  moths  stopped  to 
inspect  a  white  net  and  white  pieces  of  paper  lying  near.  The  normal 
flowers  filled  with  sugar  sirup  were  popular,  and  this  was  sipped  as  far  down 
as  available. 

Petals  obscured. — Flowers  were  covered  with  disks  of  green  crepe-paper 
with  a  hole  cut  at  the  center  to  allow  the  stamens  and  style  to  project  and 
also  to  permit  access  to  the  nectary.  Thus,  while  the  disk  covered  the  white 
petals,  it  did  not  confine  the  odor.  No  moths  or  other  visitors  stopped  at 
these  flowers,  although  the  calyx-tube  in  each  case  was  well  supplied  with 
nectar,  while  they  came  regularly  to  all  the  normal  flowers  among  which 
the  experimental  ones  were  located.  They  also  stopped  at  the  disks  of  white 
paper  that  were  grouped  among  the  normal  flowers.  As  the  supply  of  flowers 
became  greatly  reduced  at  the  end  of  the  season,  frequent  inspections  were 
made  of  the  white-paper  flowers. 

MENTZELIA  MULTIFLORA. 
NORMAL  POLLINATION. 
Habit  and  structure. — This  species  differs  from  most  of  the  others 
studied  in  that  the  flowers  open  at  about  4  o'clock  in  the  afternoon  and 
close  about  8  at  night.  There  is  a  distinct  advantage  in  opening  at  this 
time,  since  the  nectar  supply  is  running  low  in  most  of  the  flowers  visited 
during  the  day.     About  the  time  these  flowers  should  open,  several  species 

Table  42. — Visitors  and  visits  to  normal  flowers. 


Species. 

First 
day. 

Second 
day. 

4:  42 
6:  55 
2:   16 
3:     9 

5:    11 
5:   60 
7:172 
2:     9 

occidentalis 

Total 

15:122 

19:252 

MENTZELIA   MULTIFORA. 


57 


of  Bombus  and  Apis  are  seen  hovering  around  them,  landing  at  the  buds 
and  inspecting  them  carefully.  When  the  flowers  open,  the  visitors  appear 
at  once  in  fairly  large  numbers  and  immediately  commence  collecting 
both  pollen  and  nectar.  The  number  grows  less  as  the  sun  goes  down,  but 
persistent  visitors  are  present  and  working  until  dark.  This  is  particularly 
true  of  Bombus  occidentalis.  Table  42  gives  the  list  of  visitors  to  normal 
flowers  on  succeeding  days,  the  first  from  5h00m  to  6h40m  and  the  second 
from  5h00m  to  5h55m  in  the  afternoon. 


EXPERIMENTS. 

CREPE-PAPER  COROLLAS,  AND  COMPETITION. 
Crepe-paper  corollas. — Red,  white,  yellow,  green,  and  blue  paper 
corollas  were  fastened  below  the  stamens  after  the  petals  were  cut  off. 
This  was  done  about  4  p.  m.,  when  the  buds  were  beginning  to  open.  Indi- 
vidual flowers  of  Chamaenerium  and  Geranium  were  also  paired  with  these  of 
Mentzelia  in  the  group  under  observation,  so  that  competition  studies  could 
be  made  at  the  same  time.  Before  the  calendar  given  below  was  made 
the  flowers  were  observed  as  they  opened.  At  that  time  the  visitors  were 
already  in  the  vicinity,  keeping  watch  of  the  flowers.  In  putting  on  the  crepe 
corollas  the  stamens  were  exposed,  and  nectar  and  pollen  made  accessible. 
As  a  consequence,  paper  flowers  of  all  colors  were  visited,  yellow  more  than 
the  others  and  green  less  often,  doubtless  because  of  the  resemblance  to 
the  leaves.     The  yellow  flowers  so   closely  resembled  the  normal  ones 


Calendar  1. — Visits  to 


S'W  Apis  mellifica  1. 


5  01 
5  15 
5  16 


521     B 


5  25 
5  30 


Bombus  juxtus  1. 

B.  juxtus  1. 

B.  occidentalis   2    Mentzelia   of   Gera- 
nium    pairs,     6     Mentzelia     of 
Chamaenerium  pairs, 
juxtus    4    Mentzelia    of    Chamae- 
nerium pairs. 

B.  occidentalis  1. 

B.   bifarius  32;  inspects  all  crepe  and 
paired  flowers. 

B.  bifarius  27;  inspects  paired  Chamae- 
nerium. 


normal  and  crepe  flowers. 

5h45m  B.  bifarius  50;  7  Mentzelia  of  Chamae- 
nerium pairs. 

Apis  3. 

B.  bifarius  48;  inspects  all  crepe  and 
paired  flowers. 

B.  bifarius  1. 

B.  juxtus  1;  red  crepe  1,  Mentzelia 
21,  33. 

Apis  5. 

B.  bifarius  15. 


5  52 
5  55 


6  02 
6  15 


Table  43. — Summary  of  Mentzelia  calendar. 


Species. 

Normal. 

Geranium 
pair. 

Chamae- 
nerium 
pair. 

Crepe 
corollas. 

3:9 
6:173 

5:57 
1:1 

0:0 

2  (i  all) 

0:0 
2  Mentz. 

0:0 

3  (i  all) 

7  Mentz. 

4  Mentz. 
6  Mentz. 

0:0 
2    (iall) 

lr 
0:0 

Total , 

15:240 

2  Mentz.; 

2  (i  all) 

17  Mentz.; 
3  (i  all) 

1  r:2  (i  all) 

i  =  inspected;  r  =  red. 


58  NORMAL  AND  EXPERIMENTAL  POLLINATION. 

that  they  were  hard  to  find  after  these  had  opened,  and  this  similarity 
doubtless  explains  the  attraction  of  more  visitors  to  them.  After  the  normal 
flowers  opened,  those  with  artificial  corollas  were  practically  deserted,  as 
the  following  calendar  shows.  Visits  to  normal  flowers  are  indicated  by 
the  numeral  alone. 

SUMMARY. 

In  spite  of  the  numerous  visits  to  the  normal  flowers,  but  one  crepe  flower 
received  a  visit  after  the  normal  ones  opened.  Not  a  single  one  of  the  paired 
Geranium  or  Chamaenerium  flowers  was  visited,  though  19  Mentzelia  flowers 
of  such  pairs  were.  Bombus  bifarius  was  the  only  species  to  inspect  the 
artificial  or  competing  flowers,  Apis  not  even  visiting  Mentzelia  when 
paired  with  these.  This  experiment  also  included  false  flowers  made  by 
pasting  petals  of  Geranium  or  Chamaenerium  over  those  of  Mentzelia,  but 
as  these  were  noticed  only  by  one  bifarius,  which  stopped  at  a  false  Chamae- 
nerium, they  were  not  included  in  calendar  or  table. 

FRASERA  SPECIOSA. 
NORMAL  POLLINATION. 
Habit  and  structure. — The  plants  are  3  to  4  feet  tall  and  wand-like, 
growing  on  sunny  slopes  or  in  open  woods.  The  flowers  form  a  close 
cluster  often  2  feet  long,  but  the  number  of  those  open  at  any  one  time  is  not 
large  and  they  must  be  sought  throughout  the  inflorescence.  When  the 
flower  opens,  the  petals  are  curved  so  that  the  corolla  is  cup-shaped,  but 
as  the  anthers  mature,  they  are  flattened.  At  first,  the  filaments  are 
vertical  or  bend  outward  slightly,  but  they  diverge  as  the  anthers  shed 
singly  or  by  pairs;  Two  rows  of  hairs  on  a  tongue-like  projection  extend 
over  the  nectaries  and  protect  them  (plate  10). 

Behavior. — Bombus  juxtus  lands  on  the  petals  with  its  head  pointing 
toward  the  pistil.  Its  ligule  is  pushed  under  the  hairs  above  the  nectary, 
and  it  sips  in  turn  from  each.  In  doing  this  the  anther  which  extends 
between  the  two  petals  touches  the  side  of  its  abdomen.  Occasionally  this 
bee  stands  with  the  abdomen  over  the  style  and  its  head  pointing  toward 
the  outside  of  the  flower.  When  the  anthers  are  about  through  dehiscing, 
the  petals  close  up,  the  corolla  becomes  cup-shaped  again,  and  the  stamens 
project  between  the  closed  petals.  Nectar  is  still  being  produced,  and  in 
order  to  get  it  B.  juxtus  walks  up  the  outside  of  the  petals  and  dips  its  head 
into  the  inside  of  the  cup.  In  doing  this,  the  side  of  the  abdomen  and  head, 
which  have  collected  pollen  from  the  dehiscing  anthers,  rubs  pollen  against 
the  now  receptive  stigmas.  Halictus  pulzenus  walks  over  the  pistils,  then 
up  the  filaments,  and  with  its  front  legs  and  head  collects  pollen  from  the 
individual  anthers.  Clisodon  terminalis  also  comes  to  this  flower  for  pollen 
rather  than  nectar.  It  stands  on  its  hind  legs  and  collects  with  the  front 
legs  and  head.  Apis  mellifica  lands  in  such  a  manner  as  to  reach  and  empty 
the  nectaries  in  rapid  succession.  In  one  case  a  honey-bee  took  hold  of  the 
dehiscing  anthers  with  the  front  legs,  and,  while  suspended,  opened  each 
one,  scraping  out  the  pollen  and  placing  it  on  the  hind  legs. 

Fifty  flowers  were  under  observation  on  the  three  days  recorded  in 
table  44. 


FRASERA   SPECIOSA. 
Table  44. — Visitors  to  normal  flowers. 


59 


Visitors, 
35  min. 


Visitors, 
90  min. 


Visitors, 
90  min. 


Apis  mellifica 

Bombus  juxtus.  .  . 
Andrena  crataegi. 
Halictus   pulzenus 

Total 


97 


Robertson  has  discussed  the  pollination  of  Frasera  carolinensis  (1893:48) 
and  given  a  list  of  visitors  (1895:142). 

EXPERIMENTS. 

MUTILATION. 

Types. — Flowers  were  modified  in  the  following  ways:  (1)  by  removal 
of  the  stamens;  (2)  removal  of  petals  to  the  nectary;  (3)  removal  of  nectary 
hairs;  (4)  removal  of  hairs  and  pads,  leaving  only  the  nectar  pit;  (5)  removal 
of  pistil;  (6)  by  splitting  the  petals.  Observation  during  an  hour  on  July  28 
gave  the  results  shown  in  table  45  when  30  normal  flowers  and  5  of  each 
type  of  mutilation  were  used. 

Table  45. — Visits  to  normal  and  mutilated  flowers. 


Species. 

Normal. 

Nectary 

intact ; 

petals 

off. 

Stamens 
off. 

Pistil 
off. 

Hairs 
and 

sepals 
off. 

Hairs 
off. 

Petals 
split. 

Apis  mellifica 

8 
6 
0 

1 

2 
2 
0 
0 

3 
5 
0 

1 

1 
0 
0 
0 

0 
0 
0 
0 

3 
1 
3 
0 

2 

1 
0 
0 

occidentalis 

Andrena  madronitens. . .  . 

Total 

» 

4 

9 

1 

0 

7 

3:24 

While  the  number  of  visits  is  too  small  to  permit  definite  conclusions, 
mutilation  increased  them  somewhat,  probably  in  consequence  of  making 
the  nectar  easier  of  access  and  allowing  the  odor  to  escape  more  readily. 

ARTIFICIAL  AND  PAINTED  FLOWERS. 

Crepe-paper  corollas. — The  flowers  of  Frasera  are  gray-green  with 
blackish  lines  on  the  surface.  In  color  and  form  they  are  not  conspicuous, 
though  the  upright  brushes  of  hairs  above  the  nectaries  help  to  make 
them  somewhat  so.  Crepe-paper  corollas  of  red,  green,  blue,  yellow,  or 
white  were  used  to  disclose  whether  bright-colored  petals  would  make 
them  more  attractive.  The  petals  of  the  flowers  were  removed  before  the 
crepe- corollas  were  added,  and  the  latter  made  to  resemble  them  as  closely 
as  possible.  The  hairs  above  the  nectaries  were  left  intact,  so  that  the 
general  form  of  the  flower  was  the  same,  although  no  nectar  was  present. 
Bombus  juxtus  stopped  at  the  yellow  crepe  flowers  and  put  out  its  proboscis 


60 


NORMAL  AND  EXPERIMENTAL  POLLINATION. 


at  the  place  where  the  nectar  should  be.  It  felt  around  for  the  nectary, 
went  to  the  next  petal  and  did  the  same  thing,  then  to  a  red-crepe  flower 
and  repeated  this  behavior.  Apis  mellifica  avoided  the  artificial  flowers 
altogether. 

Painted  corollas. — Flowers  were  painted  blue,  yellow,  red,  green,  or 
purple  with  water-colors.  The  following  calendars  show  the  flowers 
visited  by  the  different  bees;  visits  to  normal  flowers  are  shown  by  number 
alone. 

Calendar  1. — Visitors  to  painted  flowers. 

10h45m  Apis  mellifica,  1,  blue,  1. 

10  51     Apis  mellifica,  yellow,  yellow,  2,  blue,  1. 

Andrena  crataegi,  1,  red,  3. 

Apis  mellifica,    1;   Bombus  juxtus,  1, 


10  54 
10  58 


llh05m  Apis  mellifica,  2,  blue. 

11  10  A.  mellifica,  1,  blue,  3,  blue;  Bombus 
juxtus,  1,  3,  2  yellow,  1,  red,  2, 
green,  1,  blue,  green,  blue,  1, 
green,  1. 

11  20     Bombus  juxtus,  1;  Apis  mellifica,  red,  1. 

On  the  next  day  the  same  experiment  was  repeated  with  the  following 

results : 

Calendar  2. 


11  00     Apis  mellifica,  yellow,  red,  1. 


10h47n 
10  49 


10  52 
10  56 


10h27m  Apis  mellifica,  blue,  4. 

10  28     A.  mellifica,  6,  1,  red,  3. 

10  30     A.  mellifica,  blue,  5;  Bombus  juxtus,  6. 

10  38     Bombus  juxtus,  yellow,  blue,  1 ;  Apis 

mellifica,  6,  blue,  1,  blue,  4. 
10  41     Apis  mellifica,  green,  red,  1. 
10  43     Apis  mellifica,  3. 
10  44     Halictus   pulzenus,   3;   Apis  mellifica, 

blue,  5. 

The  results  shown  by  these  two  calendars  are  summed  up  in  table  46. 
The  first  section  represents  the  visits  during  a  35-minute  period  and  the 
second  those  made  on  the  next  day,  but  covering  a  period  of  90  minutes; 
20  normal  flowers  and  5  of  each  color  were  used. 


Bombus    juxtus,     1;     Apis    mellifica, 

yellow,  green,  1. 
Apis  mellifica,  red,  yellow,  1;  Halictus 

pulzenus,  1. 
Apis  mellifica,  1,  blue,  1,  red,  1. 
Apis  mellifica,  red,  yellow,  8;  Bombus 

juxtus,  6,  6,  red. 
10  58     Apis  mellifica,  1. 


Table  46. — Summary  of  visits  to  painted  flowers. 

Species. 

Normal. 

Red. 

Blue. 

Purple. 

Yellow. 

Green. 

14 
11 

2 

1 

5 
2 
0 

0 
0 
0 

3 
2 
0 

0 
4 
0 

4 

Total 

29 

4 

7 

0 

5 

4:20 

53 

20 
4 

6 

1 
0 

6 
1 
0 

0 
0 
0 

3 
1 

0 

2 
0 
0 

Total 

77 

7 

7 

0 

4 

2:20 

106 

11 

14 

0 

9 

6:40 

The  total  number  of  visits  to  the  painted  flowers  was  less  than  half  that 
for  the  normal.  The  behavior  was  decidedly  different  for  the  two  days, 
the  bees  making  two-thirds  as  many  visits  to  the  painted  as  to  the  normal 
on  the  first,  and  only  a  fourth  as  many  on  the  second.     The  most  striking 


FRASERA   SPECIOSA.  61 

fact  with  reference  to  the  selection  of  colors  was  that  red  stood  next  to  blue, 
while  purple,  which  often  occupies  this  place,  was  completely  ignored. 

False  corollas. — Blue  corollas  were  made  from  petals  of  Campanula, 
which  were  cut  to  shape  and  glued  on  the  sepals.  The  nectaries  and  pro- 
tecting hairs  were  left  intact,  but  the  remaining  portions  of  the  Frasera  petals 
were  removed.  Fourteen  modified  and  14  normal  flowers  were  grouped  on 
the  stalk  under  observation.  The  first  Bombus  juxtus  to  visit  the  blue 
flowers  had  great  difficulty  in  finding  the  nectary,  as  well  as  a  place  on  which 
to  stand.  The  next  one  landed  on  the  blue  petals  and  thrust  out  its  ligule. 
At  9  successive  flowers  it  pushed  back  the  petals  and  tried  to  find  the 
nectary  between  these  and  the  sepals.  At  each  flower  visited  it  eventually 
found  the  nectar,  but  not  readily,  as  it  was  accustomed  to  standing  on  the 
petal  and  facing  the  pistil,  while  with  the  normal  petal  cut  away  from  around 
the  nectary  the  visitor  had  to  stand  on  a  sepal.  In  three  cases  it  finally 
straddled  the  pistil  and  dipped  its  ligule  into  the  nectaries.  Bombus  juxtus 
showed  no  objection  to  the  modified  flowers,  but  Apis  mellifica  merely 
inspected  them  without  landing. 

Calendar  3. — Visits  to  flowers  with  Campanula  petals. 


9h30m  Bombus  juxtus,  1  blue. 

9  42     Apis  mellifica,  4;  Bombus  juxtus,  3. 

9  43     Bombus  juxtus,  3  blue. 

9  48     Bombus  juxtus,  4;  Apis  mellifica,  6. 

9  51     Apis  mellifica  inspects  blue,  3,  inspects 
blue,  2. 

9  55  Bombus  juxtus,  4  blue. 
10  00  Bombus  juxtus,  6  blue,  1.  This  bee 
had  trouble  finding  the  nectar; 
it  stood  on  the  blue  petal  and 
sipped  at  the  adjoining  nectar, 
then  walked  around  the  pistil, 
taking  nectar  from  each  of  the 
others. 
10  02     Bombus  juxtus,  2,  6;  Apis  mellifica,  3. 


10h05m  B.  juxtus,  2  blue;  Apis  mellifica,  1. 

10  12  B.  juxtus,  2,  9,  6  blue,  4;  Apis  mellifica 

inspects  blue. 

10  17  B.  juxtus,  2,  5  blue. 

10  23  Apis  mellifica,  6,  inspects  blue,  3. 

10  27  A.  mellifica;  Bombus  juxtus,  3. 

10  38  Bombus  juxtus,  5  blue,  5,  3  blue,  4. 

10  42  B.  juxtus,  2,  4  blue,  1. 

10  45  B.  juxtus,  5  blue,  2. 

10  54  B.  juxtus,  6  blue,  1,  2  blue. 

10  58  B.  juxtus,  3,  2  blue,  6,  2  blue;  Apis 

mellifica  1,  inspects  blue. 

11  04  Apis  mellifica  inspects  blue. 
11  06  A.  mellifica  4. 


A  summary  shows  that  Bombus  juxtus  visited  60  normal  and  56  blue 
flowers,  while  Apis  mellifica  visited  37  normal  and  inspected  6  blue  flowers, 
but  stopped  to  visit  none  of  them. 

ADDITION  OF  NECTAR  AND  ODOR. 
Nectar. — Honey-drops  were  placed  where  the  nectaries  would  be  in 
normal  flowers,  and  were  also  added  to  those  with  crepe  corollas.  Bombus 
juxtus  and  Apis  mellifica  were  working  constantly  on  the  flowers  in  this 
location.  In  normal  flowers  they  went  directly  to  the  nectaries,  sipping 
nectar  from  all  four,  but  the  paper  flowers  were  avoided,  even  though  they 
had  honey-drops  on  them.  The  honey-drops  on  normal  flowers  were 
visited  by  2  Apis  mellifica  and  1  Bombus  juxtus,  but  they  were  not  sufficiently 
attractive  to  bring  about  a  return  visit. 

SUMMARY. 

Mutilation  increased  visits  somewhat,  owing  chiefly  to  the  behavior 
at  the  flowers  with  the  stamens  or  the  nectary  hairs  removed.  The  response 
of  Bombus  and  Apis  to  artificial  flowers  was  fairly  typical,  the  one  working 
on  them  industriously,  the  other  ignoring  them  entirely.     In  the  case  of 


62 


NORMAL  AND  EXPERIMENTAL  POLLINATION. 


painted  flowers,  both  went  readily  from  these  to  the  normal  or  the  reverse, 
the  ratio  for  Apis  being  27:67  and  for  Bombus  12:31,  or  almost  identical 
in  value.  The  false  flowers  made  of  Campanula  petals  were  treated  like 
the  paper  ones,  Bombus  visiting  practically  as  many  of  them  as  the  normal 
and  Apis  merely  inspecting  them  without  landing.  Honey  received  little 
attention  from  either,  the  paper  flowers  with  honey-drops  being  entirely 
ignored. 

MERTENSIA  PRATENSIS. 
NORMAL  POLLINATION. 
Behavior. — The  flowers  are  pendant  and  have  a  tubular  corolla  with 
a  bell-shaped  expansion  below  (plate  11).  The  corolla-tube  is  only  about 
15  mm.  long,  but  both  Vespa  germanica  and  Bombus  juxtus  often  bore  holes 
at  the  base  of  the  corolla  and  steal  nectar.  They  land  on  the  corolla-tube 
with  their  hind  legs  toward  the  corolla  mouth.  Juxtus  carries  yellow  pollen 
on  its  legs,  probably  from  Fragaria  or  Rubus  strigosus  previously  visited, 
but  it  does  not  gather  pollen  at  Mertensia.  It  comes  to  this  for  nectar, 
and  upon  landing  it  hangs  on  to  the  pendant  corolla-tube,  pushes  out  its 
ligule,  and  at  once  takes  nectar.  Edwardsi  enters  the  flower,  resting  on  the 
lower  lobe  of  the  corolla,  and  its  head  is  pushed  into  the  tube  for  the  nectar. 
While  the  stigma  comes  in  contact  with  the  abdomen  and  receives  the 
pollen  found  there,  its  head  brushes  against  the  dehiscing  anthers  and  col- 
lects pollen.  Osmia  pentstemonis  is  so  eager  for  nectar  that  it  opens  buds 
and  pushes  its  head  into  the  corolla-tube  to  secure  it.  Andrena  madronitens 
usually  rifles  flowers  of  nectar  when  a  hole  has  already  been  made.  Other- 
wise, it  pushes  its  head  directly  into  the  tube,  bending  at  the  thorax 
so  that  the  abdomen  is  outside  the  corolla-tube  and  pointing  upward. 
Halictus  pulzenus  lands  at  the  corolla  mouth,  eats  pollen,  and  then  goes  to 
the  base  of  the  corolla  to  puncture  it  for  nectar.  Other  species  of  Halictus 
push  far  into  the  corolla  tube,  where  they  scrape  pollen  so  vigorously  with 
the  hind  legs  that  it  flies  out  of  the  opening.  While  doing  this,  the  head 
is  very  near  the  nectar,  probably  sipping  it,  and  the  hind  legs  are  resting  on 
the  anthers.  Halictus  (Evylaeus)  sp.  bends  over  the  edge  of  the  corolla -tube, 
while  its  head  is  in  contact  with  the  stamens,  and  touches  the  stigma  as  it 
leaves  the  flower.  Dejeania  vexatrix  lands  and  rests  its  legs  on  the  lower 
edge  of  the  petals,  while  it  pushes  its  head  into  the  corolla-tube  and  sucks 

Table  47. — Visitors  to  normal  flowers. 


Species. 

Observation. 

Species. 

Observation. 

1 

2 

1 

2 

49 
6 

4 
3 

1 
2 
0 

0 
0 
4 
0 
3 
0 
1 

Halictus  (Evylaeus)  sp 

Monumetha  albifrons 

0 
0 
0 
0 
0 

Pseudomasaris  vespoides 

Total 

70 

8 

CASTILLEIA   MINIATA.  63 

nectar.  Acmaeops  longicornis  enters  the  corolla  and  eats  pollen,  which  it 
also  collects  and  deposits  as  it  moves  slowly  about.  Selasphorus  platycercus 
visits  and  pollinates  Mertensia  as  it  flies  very  rapidly  from  flower  to  flower. 

In  table  47  two  lists  of  visitors  are  given.  The  first  represents  those 
present  during  a  two-hour  period  in  the  midst  of  the  flowering  season,  the 
second  those  for  an  hour  period  at  the  end  of  the  season.  In  each  case  100 
flowers  were  under  observation. 

During  another  hour's  observation  toward  the  end  of  the  season,  15 
individuals  of  Bombus  juxtus  made  167  visits  to  140  flowers.  The  only 
other  visitors  were  two  wasps  that  robbed  the  flowers. 

EXPERIMENTS. 

MUTILATION. 
Changes  of  corolla. — The  petals  were  split  apart,  the  corolla  made 
irregular,  or  the  upper  petals  were  removed  in  various  flowers.  The  only 
visitors  during  the  period  of  observation  were  4  individuals  of  Halictus  sp., 
which  went  to  the  flowers  with  the  front  half  of  the  petals  removed.  They 
paid  no  attention  to  the  exposed  stamens  and  nectar,  but  pierced  the  small 
corolla-tube  in  the  usual  place,  as  when  robbing  normal  flowers. 

CASTILLEIA  MINIATA. 
NORMAL  POLLINATION. 
Habit  and  structure. — The  bracts  inclosing  the  flowers  are  vermilion 
in  color  and  arranged  in  a  closely  massed  spike.  As  the  individual  flowers 
mature  they  elongate  rapidly  and  take  an  ascending  position.  The  first 
pair  of  anthers  ripen  while  the  flower  is  still  very  small,  about  one-third 
the  mature  size.  The  lower  lip  is  much  suppressed  and  serves  to  open  the 
slit  when  pulled  down.  When  the  anthers  are  about  through  dehiscing, 
the  style  elongates,  grows  through  the  tip  of  the  corolla-tube,  and  then 
bends  downward.  To  obtain  nectar,  visitors  must  push  into  the  slit  of  the 
corolla  and  reach  to  the  base  of  the  tube.  In  doing  this  the  head  comes  in 
contact  with  the  anthers  in  young  flowers,  while  in  the  more  mature  ones 
the  stigma  bends  downward  so  that  it  rubs  the  back  of  the  visitor  (plate  13). 

Behavior. — Halictus  (Evylaeus)  sp.  transfers  pollen  from  the  under  part  of 
its  abdomen  to  the  receptive  stigma  as  it  lands  on  the  green  tip  of  the  corolla. 
It  then  turns  upside  down,  opens  the  corolla,  and  exposes  the  stamens. 
With  its  front  legs  it  scoops  out  the  pollen  and  places  it  on  the  ventral 
surface  of  the  abdomen.  One  individual  stood  with  its  head  at  the  lower 
lip  of  the  corolla  and  took  out  pollen  with  its  front  feet  and  mouth-parts. 
A  second  landed  with  the  head  toward  the  style  and  tried  to  open  the  corolla 
slit  without  success;  it  then  turned  toward  the  other  end  and  scraped  up 
the  pollen  on  the  outside  with  its  front  legs,  placing  it  on  the  rear  legs  and 
abdomen.  After  turning  again,  it  repeated  its  unsuccessful  attempt  to 
open  the  corolla,  then  turned  its  head  downward,  and  at  the  lower  lip 
succeeded  in  opening  the  corolla.  It  went  into  the  latter  until  only  the 
abdomen  tip  was  visible  outside  the  flower.  A  third  bee  of  this  species 
landed  at  the  tip  of  the  corolla  and  ate  pollen  found  on  the  outside.  The 
slit  of  this  flower  was  inverted,  i.  e.,  faced  up.     The  bee  walked  to  the  under 


64  NORMAL  AND  EXPERIMENTAL  POLLINATION. 

side  to  the  position  in  which  it  was  accustomed  to  work,  looked  around,  and 
found  no  slit.  It  had  difficulty  in  holding  on  to  the  under  side  in  the  absence 
of  the  slit.  It  then  moved  to  the  dorsal  side  and  found  a  few  grains  of 
pollen,  but  did  not  seem  satisfied.  Again  it  tried  the  ventral  side  of  the 
corolla  and  looked  all  around  for  the  slit  and  the  lower  lip.  It  went  to  the 
dorsal  side  again,  but  failed  to  locate  the  slit.  For  a  third  time  it  moved 
to  the  under  side  of  the  corolla,  but  not  finding  what  it  was  looking  for, 
flew  away  to  a  flower  in  a  normal  position  and  located  the  slit  at  once. 
A  fourth  one  landed  with  its  head  toward  the  style,  walked  to  the  end  of  the 
latter  and  over  it,  the  style  touching  the  pollen  loads  on  its  legs,  and  then 
walked  back  again.  It  worked  for  several  seconds  with  its  head  and  the 
first  pair  of  legs  in  the  attempt  to  open  the  slit,  and  finally  succeeded. 
A  fifth  individual  alighted  on  the  lower  lip  and  immediately  went  down  into 
the  corolla  and  sucked  nectar.  Then  it  turned  around,  walked  out  to  the 
end  of  the  style,  which  swayed  under  its  weight,  and  around  it.  It  returned 
to  the  end  of  the  corolla  and  then  backed  out  onto  the  stamens,  where  it 
collected  pollen,  placing  it  on  the  hind  legs  before  flying  away. 

Selasphorus  platycercus  landed  upon  a  low  tree  branch  and  sucked 
nectar  from  the  nearby  Castilleia  flowers,  while  resting  its  wings.  Normally, 
it  keeps  its  feet  close  to  the  body  and  sustains  itself  in  the  air  by  rapid  wing 
motion  while  sucking  nectar.  In  one  flower  the  corolla  tube  was  too  small 
even  for  its  slender  bill.  The  bird  found  no  trouble  in  thrusting  the  bill 
into  the  corolla,  but  was  unable  to  pull  it  out  again.  It  then  lowered 
itself  so  that  the  corolla  tube  became  pendant  and  sipped  more  nectar, 
finally  freeing  itself  after  further  effort. 

The  normal  visitors  to  Castilleia  are  not  numerous,  observations  for  a 
period  of  2  hours  and  20  minutes  yielding  only  the  following:  Halictus 
pulzenus  6,  Sphecodes  sp.  2,  Selasphorus  platycercus  3. 

Merritt  (1897:21)  states  that  the  flowers  of  Castilleia  affinis  have  abun- 
dant honey,  and  that  pollination  is  usually  effected  before  the  flowers  attain 
their  full  length.  The  exserted  capitate  stigma  is  struck  by  the  visiting 
humming-bird,  while  the  bill  receives  a  fresh  supply  of  pollen  from  the 
anthers  just  below  in  the  galea.  Longyear  (1909:79)  has  described  the 
structure  and  pollination  of  the  flower  of  C.  linarifolia. 

EXPERIMENTS. 

MUTILATION. 
Upper  lip  removed,  spike  inverted. — The  upper  lip  of  the  corolla 
was  cut  off  even  with  the  lower,  the  bract  cut  back  to  the  same  length, 
and  the  cluster  then  inverted  so  that  the  lower  lip  of  the  flower  was  turned 
up.  Halictus  pulzenus  landed  and  remained  quiet  at  the  lower  lip  for 
some  time,  with  its  head  inside  the  corolla.  It  was  probably  sucking 
nectar,  but  there  was  no  movement  of  the  abdomen  to  indicate  this.  It 
then  walked  out  on  the  filaments  to  the  anthers  and  ate  the  pollen  that 
was  still  there.  It  next  went  to  the  end  of  the  style,  arching  its  body  over 
in  such  a  way  that  the  stigma  rubbed  against  the  abdomen. 

PAINTED  FLOWERS. 
Painted  bracts. — The  bracts  of  various  clusters  were  painted  purple, 
green,  or  yellow  with  water-colors.     A  humming-bird  sucked  nectar  from 


PENTSTEMON   GLABER.  65 

such  flowers  in  the  normal  fashion  and  Halictus  pulzenus  likewise  gave  no 
evidence  of  being  disturbed  by  the  change. 

PENTSTEMON  GLABER. 
NORMAL  POLLINATION. 
Habit  and  structure. — The  plants  of  this  species  usually  grow  in  small 
communities  on  warm  gravel-slides.  The  stems  are  about  a  foot  high, 
several  in  number  and  ascending.  The  flowers  are  arranged  in  brilliant 
secund  clusters.  This  is  one  of  the  large-flowered  species,  with  not  only  a 
comparatively  large  corolla  mouth,  but  also  a  tube  of  nearly  the  same  size. 
Hence,  its  nectar  is  the  most  accessible  of  all  the  species  of  this  genus  in  the 
region.  The  staminode  is  broadly  spatulate  and  covered  for  nearly  half 
its  length  with  long  hairs  in  two  rows.  The  flowers  are  protandrous,  the 
anthers  on  the  longer  filaments  maturing  first  and  arching  above  the  entrance 
to  the  corolla  mouth.  The  young  stigma  is  straight,  extending  forward 
just  behind  the  front  pair  of  anthers.  When  the  stigmas  become  receptive, 
the  four  anthers  are  nearly  through  dehiscing  and  the  style  elongates,  its 
tip  arching  sharply  downward  between  the  front  pair  of  anthers  and  almost 
touching  the  staminode.  In  older  flowers  the  staminode  coils  inward, 
coming  in  contact  with  the  stigmas  (plates  12  and  17). 

Behavior. — Osmia  phaceliae  works  persistently  at  the  tip  of  the  bud, 
trying  to  gain  entrance  to  the  corolla.  When  the  flower  is  about  ready  to 
bloom,  the  bee  succeeds  in  opening  it.  In  mature  flowers  it  stands  at  the  corolla 
entrance  and  scratches  the  dorsal  surface  of  its  thorax  on  the  anthers, 
and  then  goes  into  the  corolla-tube  and  secures  nectar.  Osmia  pentstemonis 
lands  where  the  lobes  of  the  lower  lip  bend  downward ;  it  usually  comes  for 
pollen  and  enters  the  flower  to  the  point  where  the  anthers  brush  against  the 
thorax.  The  latter  is  first  well  rubbed  on  the  front  pair  of  anthers  and  then 
on  the  rear  ones.  Its  dorsal  surface  rubs  back  and  forth  against  the  anthers 
until  the  stigmas  as  well  as  the  scopa  become  white  with  pollen.  It  rarely 
if  ever  seeks  both  pollen  and  nectar,  but  some  individuals  pass  the  anthers 
and  take  nectar  only.  Osmia  melanotricha  collects  pollen  in  the  same  manner, 
ignoring  the  nectar,  in  spite  of  the  fact  that  the  corolla-tube  is  nowhere  so 
narrow  that  it  could  not  obtain  this  with  its  short  tongue.  Osmia  densa 
is  so  large  that  its  body  fills  the  entire  corolla,  the  tip  of  the  abdomen  reaching 
to  the  corolla  mouth.  It  comes  for  nectar  and  the  under  surface  of  its 
abdomen  rubs  the  staminode  while  it  is  sipping.  In  more  mature  flowers 
with  a  curved  style,  the  stigma  brushes  closely  against  its  back.  In  seeking 
nectar,  Osmia  coloradella  lands  on  the  lower  petals  and  stands  upright, 
bringing  about  pollination  by  contact  with  its  dorsal  surface. 

Vespa  germanica  stands  at  the  angle  of  the  corolla  mouth  and  rubs  the 
thorax  against  the  anthers  so  hard  that  a  scratching  sound  is  heard,  while  it 
moves  back  and  forth  5  to  10  times  during  the  process.  The  hairs  on  its  head 
touch  the  anthers  and  stigma  as  it  sucks  nectar.  Just  before  leaving  the 
flower,  it  stands  at  the  edge  of  the  corolla  mouth  and  with  the  front  legs 
scrapes  off  and  eats  the  pollen  that  has  fallen  on  its  head.  Andrena  madro- 
nitens  goes  into  the  flowers  upside  down  and  collects  pollen  only,  while  A. 
vicina  enters  for  nectar  alone  and  remains  for  a  long  time  at  each  flower. 


NORMAL  AND  EXPERIMENTAL  POLLINATION. 


Prosopis  varifrons  is  very  small  in  comparison  with  the  size  of  the  tube,  and 
some  individuals  go  directly  to  the  nectary  and  depart  without  touching  the 
anthers.  Others  work  upside  down  and  eat  pollen  as  they  hang  suspended 
from  the  anthers,  without  making  any  attempt  to  find  the  nectary.  Halic- 
tus  pulzenus  lands  on  the  lower  lip,  then  walks  to  the  upper  one  and  stands 
upside  down  on  the  anthers.  The  tip  of  its  abdomen  is  just  below  these 
while  it  is  removing  pollen  with  its  front  legs.  It  also  picks  up  and  eats 
any  pollen  that  has  dropped  on  the  lower  lip. 

Bombus  juxtus  lands  in  the  normal  way,  turns  upside  down,  and  takes  a 
position  such  that  the  anthers  rub  the  thorax  as  it  moves  back  and  forth. 
It  also  scrapes  pollen  from  the  anthers  with  its  front  legs  and  transfers  it  to 
the  hind  ones.  This  bee  often  tries  very  hard  to  open  buds  and  turns  over 
and  around  in  the  attempt  to  do  this.  Bombus  bifarius  goes  into  a  corolla- 
tube,  turns  upside  down,  and  scrapes  pollen  from  the  anthers  with  its  front 
legs,  placing  it  on  the  hind  ones.  Monumetha  albifrons  lands  and  goes 
directly  to  the  nectar.  Its  thoracic  hairs  brush  the  anthers  as  it  sucks 
nectar  and  some  pollen  is  collected  accidentally,  but  it  makes  no  effort  to 
gather  it.  Titusella  pronitens  works  on  the  anthers  only,  standing  upside 
down  as  it  collects  pollen  on  its  scopa. 

Table  48. — Visitors  to  normal  flowers. 


Species. 

Observations. 

1 

2 

3 

4 

5 

6 

63 

48 
3 
1 
1 
3 
0 
0 
1 
0 

42 
10 
0 
0 
0 
1 
3 
0 
0 
1 

1 

7 
0 
0 
0 
0 
2 
0 
0 
0 

6 

34 
0 
0 
0 

4 
0 

1 
0 

1 

2 
17 
0 
0 
0 
0 
1 
0 
0 

1 

2 
4 
0 
0 
0 
0 
4 
0 
0 

1 

Total 

120 

57 

10 

46 

21 

11 

COMPARATIVE  VALUES. 

21 
16 

16 
3 

2 
14 

4 
22 

4 
34 

1 

3 

Total 

40 

21 

20 

31 

40 

8 

Calendars. — Table  48  contains  the  results  of  observations  on  six  dif- 
ferent days.  There  were  150  open  flowers  under  observation  on  the  first 
date,  172  on  the  second,  and  100  on  the  others.  The  records  were  made 
at  the  following  times:  (1)  June  25,  8  to  10  a.  m.;  (2)  June  27,  lh40m  to  3h18m 
p.  m.;  (3)  June  28,  10h35m  to  llh04ra  a.  m.;  (4)  July  13,  10  to  llh30m  a.  m.; 
(5)  July  24,  llh06m  to  llh40m  a.  m.;  (6)  July  1,  9h15m  to  10h40m  a.  m. 


PENTSTEMON   GLABER. 


67 


While  the  first  part  of  table  48  contains  the  actual  record  of  visits,  the 
exact  significance  of  these  can  be  obtained  only  by  reducing  them  to  the 
same  basis  as  to  length  of  observation  and  number  of  flowers.  This  reveals 
a  variation  of  five  times  in  the  total  number  of  visits  per  hour.  More 
suggestive,  however,  is  the  balance  between  Pseudomasaris  and  Osmia; 
the  decrease  of  the  one  with  the  increase  of  the  other  indicates  the  effect 
of  competition  for  the  same  species,  either  actually  in  progress  or  wrought 
out  in  the  seasonal  behavior. 

Observations  1  and  2  in  table  49  give  the  lists  of  visitors  from  10  to 
10h40m  on  two  mornings  a  week  apart  with  50  flowers  concerned  in  each 
case.  There  were  19  flowers  in  number  3,  which  was  made  on  June  27 
from  llh20m  to  12  a.  m.  Observation  4  was  taken  on  July  10  from  9h47m 
to  10h26m  on  20  flowers.  50  flowers  were  used  for  5,  which  was  on  July  12 
from  10  to  llh30m  a.  m.  Number  6  was  made  July  18  from  10h4m  to 
llh40m  and  50  flowers  were  in  the  group  under  observation.  As  usual, 
the  first  number  in  each  column  indicates  the  visitors,  the  second  the 
visits  made. 


Table  49. — Visitors  and  visits  to  normal  flowers. 


Species. 


Observation. 


Osmia  phaceliae 

bruneri 

Pseudomasaris  vespoides 

Clisodon  terminalis 

Melissodes  fremonti 

Andrena  vicina 

Prosopis  varifrons 

elliptica 

Apis  mellifica 

Bombus  juxtus 

Halictus  pulzenus 

Thanaos  martialis 

Total 


26:65 
2:2 
6:18 
6:25 
2:4 
2:3 
2:2 
2:2 
1:2 
1:32 
0:0 
0:0 


17:20 
0:0 
3:4 
3:9 
0:0 


2:2 
2:2 
1:1 


0:0 

4:9 

8:51 

0:0 

0:0 

0:0 

1:1 

0:0 

0:0 

2:2 

0:0 

0:0 


0:0 

1:8 

5:113 

0:0 

0:0 

0:0 

1:1 

0:0 

2:2 

1:1 

1:1 

0:0 


0:0 
27:71 
4:17 
6:25 
2:2 
0:0 
2:2 
0:0 
1:2 
1:30 
0:0 
0:0 


15:63 


11:126 


43:149 


0:0 
17:20 
4:4 
1:8 
0:0 
1:5 
0:0 
0:0 
0:0 
4:4 
0:0 
0:0 


27:41 


COMPARATIVE  VALUES. 


Osmia  phaceliae 

bruneri 

Pseudomasaris  vespoid 
Clisodon  terminalis .  .  . 
Bombus  juxtus 

Total 


39:87 
3:3 
9:27 
9:37 
1:48 


25:30 
0:0 
4:6 
4:13 


0:0 
18:40 
36:225 

0:0 

9:0 


75:233 


45:64 


66:282 


0:0 

4:36 

22:510 

0:0 

4:4 


48:570 


0:0 
18:47 
3:12 
4:17 
1:20 


30:103 


0:0 
25:40 


2:16 


The  reduction  in  the  number  of  visitors  and  the  great  decrease  in  the 
visits  made  by  them  shown  by  the  second  observation  were  due  entirely 
to  the  wind,  the  other  factors  being  essentially  the  same.     A  similar  decrease 


68 


NORMAL  AND  EXPERIMENTAL  POLLINATION. 


in  the  number  of  visits  particularly  occurred  toward  the  end  of  the  flowering 
period,  as  shown  in  columns  5  and  6.  The  dominance  of  the  species  of 
Osmia  alternates  in  a  striking  and  suggestive  manner.  A  similar  alternation 
occurs  in  the  case  of  Pseudomasaris  and  Clisodon,  and  the  whole  summary 
shows  the  extent  to  which  the  maxima  for  different  species  tend  to  fall  at 
different  times.  The  varying  effectiveness  of  the  genera  is  revealed  by  a 
comparison  of  Bombus  and  Osmia;  2  individuals  of  the  former  visited  30 
and  32  flowers  respectively  on  the  same  days  that  those  of  Osmia  averaged 
but  2.5  visits  each. 

Merritt  (1897:19)  found  that  Pentstemon  palmeri,  P.  barbatus  labrosus, 
and  P.  bridgesi  all  have  abundant  nectar  secreted  by  the  bases  of  the  two 
upper  stamens.  The  filaments  of  these  curve  inward  to  meet  each  other 
and  the  other  pair  of  filaments,  and  then  rise  to  the  upper  wall.  The 
staminode  crosses  the  tube  above  this  junction  and  lies  for  the  rest  of  its 
length  on  the  lower  wall,  thus  excluding  short-tongued  visitors  from  the 
nectaries.  Dehiscence  of  the  anthers  is  not  simultaneous,  and  it  is  continued 
for  some  time,  the  style  lengthening  only  toward  its  close.  The  latter 
lies  against  the  upper  side,  but  is  curved  to  bring  the  stigma  down  to  the 
entrance,  but  out  of  the  line  of  falling  pollen.  P.  palmeri  is  constricted 
in  the  tube  where  the  4  filaments  meet  about  4  mm.  above  the  base,  and  the 
sterile  filament  crosses  just  above  this.  The  throat  and  limb  are  wide 
enough  to  admit  the  largest  bees.  The  anthers  lie  against  the  upper  wall 
and  the  heavily  bearded  staminode  forces  insects  against  them,  though  one 
frequent  guest,  Osmia  densa,  appears  to  get  nectar  without  touching  them. 
The  vivid  scarlet  of  P.  barbatus  labrosus  stamps  it  as  a  humming-bird 
flower.  The  anthers  are  exserted  but  protected  by  the  upper  lip,  and  serve 
to  guard  the  entrance,  as  the  stigma  does  later.  Honey-bees  and  Antho- 
phora  sometimes  collect  pollen  from  the  anther-slits.  In  P.  bridgesi  honey- 
bees attempted  to  reach  the  nectar,  but  in  vain,  while  the  pollen  is  dis- 
charged too  slowly  to  tempt  bees. 

EXPERIMENTS. 
CHANGE  OF  POSITION. 

Racemes  inverted. — Table  50  gives  a  summary  of  the  results  of  an 
experiment  in  which  23  racemes  in  the  normal  position  and  3  inverted 
ones  were  under  observation. 

Table  50. — Visitors  to  normal  and  inverted  racemes. 


Specie3. 


Normal. 


Inverted. 


Relative  No. 
inverted. 


Osmia  phaceliae 

bruneri 

Bombus  juxtus 

Apis  mellifica 

Pseudomasaris  vespoides 
Melissodes  f remonti .... 
Prosopis  varifrons 

Total 


118 


PENTSTEMON   GLABER.  69 

Since  there  were  about  7  times  as  many  flowers  in  the  normal  position 
as  inverted,  the  latter  were  relatively  about  a  third  more  attractive,  the 
ratio  being  118:169. 

In  another  series  of  observations  the  behavior  of  certain  individuals 
was  noted  in  detail,  especially  for  Osmia,  Vespa,  and  Apis,  The  first 
individual  of  Osmia  phaceliae  landed  on  the  new  lower  lip,  then  climbed  to 
the  upper,  went  in  upside  down,  and  scratched  its  thorax  back  and  forth 
on  the  stamens.  At  the  next  inverted  flower  it  landed  in  the  same  way, 
looked  around,  and  backed  out.  The  second  went  to  4  inverted  flowers, 
where  it  scraped  its  thorax  against  the  inverted  staminode  and  then  pushed 
in  to  where  the  nectar  should  be.  The  third  went  straight  in  and  tried 
to  find  the  opening  to  the  nectary,  but  did  not  succeed.  The  fourth  indi- 
vidual entered  the  inverted  flowers  just  as  the  normal  ones  and  stayed  the 
same  length  of  time,  while  the  fifth  attempted  to  enter  3  inverted  flowers 
without  success.  The  sixth  went  into  3  inverted  flowers  and  obtained 
nectar  with  but  little  more  difficulty  than  in  normal  ones,  but  the  seventh 
entered  upside  down,  hence  in  its  usual  position  with  respect  to  the  flower 
parts,  and  consequently  worked  as  usual.  Four  others  then  did  the  same 
in  succession.  Osmia  phaceliae  often  went  into  inverted  flowers  and 
scratched  its  thorax  against  the  staminode,  evidently  without  realizing 
that  it  was  not  touching  the  anthers.  Some  of  this  species  at  once  recog- 
nized that  the  flowers  were  inverted  and  landed  accordingly.  Osmia 
melanotricha  also  went  into  such  flowers  upside  down  and  secured  nectar. 
It  entered  and  scraped  pollen  as  in  normal  flowers. 

Vespa  germanica  twice  tried  unsuccessfully  to  find  nectar  in  these  flowers. 
It  landed,  but  before  entering  noticed  something  different  and  went  to  the 
next  flower,  which  was  also  inverted,  where  it  behaved  in  the  same  way. 
A  second  individual  entered  hesitatingly  in  such  a  manner  that  it  was  upside 
down  and  then  took  nectar.  A  third  one  flew  above  and  examined  6  inverted 
blossoms  but  did  not  land,  while  a  fourth  wasp  entered  the  flower,  and 
reached  into  the  nectary,  but  did  not  stay  long  enough  to  get  nectar.  It  then 
flew  past  the  mouths  of  other  inverted  flowers,  but  did  not  land.  Apis  melli- 
fica  went  into  2  inverted  flowers,  but  departed  at  once.  It  stopped  several 
times  at  such  flowers  later,  but  noticed  the  difference  and  flew  away. 
Finally,  it  came  back  to  a  stem  bearing  inverted  flowers  and  obtained  pollen 
without  standing  upside  down.  Another  individual  stood  upright  and 
gathered  pollen  from  the  anthers  underneath  these  flowers  instead  of 
standing  upside  down.  Clisodon  terminalis  visited  10  normal  flowers 
and  4  inverted  ones,  but  obtained  nectar  in  but  2  of  the  latter,  while  Andrena 
vicina  secured  it  as  usual. 

When  the  two  lobes  of  the  lower  lip  in  an  inverted  flower  were  cut  into 
separate  petals,  Osmia  melanotricha  landed  easily,  but  the  stamens  and  style 
which  projected  in  front  of  the  flower  confused  it  so  that  it  could  not  find 
the  entrance  to  the  nectar.  Osmia  pentstemonis  likewise  landed  on  the  in- 
verted upper  lip,  but  did  not  find  the  anthers  and  nectar.  In  the  case  of 
inverted  flowers  with  the  corolla  mouth  closed  by  wilting,  it  succeeded  in 
opening  the  corolla  with  difficulty,  but  failed  to  find  the  anthers  and  so 
flew  out  at  once. 


70  NORMAL  AND  EXPERIMENTAL  POLLINATION. 

Racemes  horizontal. — Bombus  juxtus  landed  at  the  corner  of  the 
mouth,  turned  sideways,  and  then  sucked  nectar  in  the  normal  position  with 
relation  to  the  flower.  Osmia  pentstemonis  tried  to  enter  3  flowers  with  the 
corolla  tip  pointing  up,  but  after  landing  and  starting  in,  it  backed  out 
each  time  without  finding  the  anthers.  The  next  individual  went  into  these 
flowers  apparently  without  noticing  the  change  in  position.  0.  melanotricha 
was  puzzled  by  those  that  had  the  corner  of  the  mouth  pointing  up. 
It  landed  by  placing  the  right  legs  on  the  lower  outside  lobe  of  the  upper 
lip  and  the  left  legs  on  one  of  the  lower,  thus  straddling  the  angle  of  the 
mouth,  which  pointed  down.  The  bee  then  moved  back  and  forth,  trying  to 
rub,  and  some  time  elapsed  before  it  discovered  that  the  anthers  were 
missing,  when  it  flew  away. 

MUTILATION. 

Cotton  at  the  corolla  mouth. — Absorbent  cotton  was  placed  in  the 
corolla  mouth,  thus  obscuring  the  anthers  and  blocking  the  entrance  to 
the  nectaries.  The  amount  of  cotton  used  was  small  and  it  was  placed  in 
position  lightly,  so  that  insects  could  easily  push  it  aside  and  gain  entrance 
to  the  flowers  if  they  made  any  effort  to  do  so.  Half  of  the  racemes  were 
left  normal  and  those  with  obstructed  corollas  were  arranged  at  various 
places  in  the  cluster.  Two  individuals  of  Osmia  pentstemonis  hovered  at 
the  corolla  mouth,  but  did  not  try  to  force  an  entrance.  Osmia  phaceliae 
attempted  repeatedly  to  get  in  past  the  corolla  mouth  but  did  not  succeed, 
while  Vespa  germanica  noticed  the  change  just  as  it  landed  and  did  not  try 
to  enter. 

Styles,  stamens,  and  staminode  removed. — In  flowers  thus  modified, 
Bombus  juxtus  started  to  enter  one,  but  before  turning  upside  down  noticed 
the  difference  and  went  to  the  next  flower.  Osmia  bruneri  flew  to  the 
corolla  mouth,  but  noticed  the  change  and  did  not  enter,  while  0.  phaceliae 
reached  the  point  of  getting  its  head  in  position  to  suck  nectar  before 
flying  away.  Another  individual  went  into  the  flower,  worked  as  usual, 
and  left,  apparently  without  having  noted  the  change. 

Corolla  split. — When  the  corolla  was  deeply  split  between  the  lips, 
Andrena  vicina  visited  3  flowers  without  noting  the  difference.  The  first 
Halictus  pulzenus  that  arrived  walked  around  the  flowers,  but  without 
entering.  Another  landed  on  the  lowest  lobe  of  the  corolla  and  wandered 
back  and  forth  over  the  edge.  It  then  walked  over  the  lowest  lobe  5  times, 
trying  to  find  the  way  into  the  corolla,  and  then  flew  away  without  entering 
at  all.  Some  individuals  of  Bombus  juxtus  stopped  and  sucked  nectar  as 
if  they  noted  no  change,  while  others  flew  away  at  once  as  if  frightened. 
Clisodon  terminalis  worked  in  the  normal  way,  and  both  Vespa  germanica 
and  Pseudomasaris  vespoides  went  directly  to  the  nectary,  took  nectar, 
and  departed.  One  Osmia  pentstemonis  landed  and  went  at  once  to  the 
nectary,  but  flew  away  without  sipping.  Another  alighted  on  the  lower 
petal  and  walked  around,  but  since  the  anthers  were  projecting  in  front  of 
the  flower  and  the  corolla  lips  were  somewhat  reflexed,  it  failed  to  find  the 
anthers  and  the  tip  of  the  staminode,  which  it  usually  uses  as  a  guide  to  the 
nectary.  Osmia  phaceliae  went  to  9  flowers,  among  which  was  one  with 
the  corolla  lips  separate.     This  bee  advanced  to  the  nectar,  but  suddenly 


PENTSTEMON   GLABER.  71 

flew  away  as  if  aware  of  the  change.  Another  individual  went  into  3  of 
these  flowers  and  inserted  its  ligule  into  the  nectary,  but  left  without  taking 
nectar  (plate  17). 

Corolla  lips  separated  and  staminode  raised. — In  flowers  of  this 
type,  Osmia  phaceliae  tried  repeatedly  to  get  on  the  lower  lip  of  the  corolla, 
but  slipped  off.  Finally  it  landed  and  then  bumped  into  the  staminode. 
After  doing  this  twice  it  went  in  at  the  side  and  obtained  nectar.  In 
normal  flowers  0.  melanotricha  has  the  habit  of  rubbing  its  back  against  the 
anthers,  but  in  these  it  failed  to  find  them,  and  went  instead  to  the  nectary. 

Upper  lip  removed  at  the  throat. — Osmia  bruneri  landed  as  usual 
and  secured  nectar,  the  style  touching  its  back  in  the  process. 

Lower  lip  shortened  half. — The  lower  lip  constitutes  the  landing- 
platform,  and  this  experiment  was  devised  to  find  out  the  response  of  visitors 
when  it  was  removed.  Clisodon  terminalis  went  into  a  flower  without  noting 
the  change;  it  then  flew  to  a  normal  flower,  and  afterward  to  one  with  the 
corolla  mouth  obstructed  with  cotton.  When  it  did  not  succeed  in  entering 
this,  it  flew  away.  Vespa  germanica  sipped  some  nectar,  but  did  not  stay 
the  usual  time.  Osmia  phaceliae  landed  on  the  staminode,  finding  difficulty 
in  balancing  itself,  but  finally  made  its  way  along  the  staminode  until  it 
obtained  a  better  foothold  on  the  corolla-tube  and  was  able  to  reach  the 
nectar. 

Lower  lip  removed. — Osmia  melanotricha  entered  these  flowers  by 
straddling  the  staminode  and  was  able  to  secure  nectar. 

Lower  lip  and  part  of  tube  removed. — The  lobes  of  the  lower  lip 
were  removed,  as  well  as  the  tube  for  a  distance  of  4  mm.  Osmia  bruneri 
succeeded  in  landing  after  repeated  attempts  by  taking  hold  of  the  anthers 
with  the  front  legs,  turning  upside  down,  and  walking  a  short  distance  into 
the  flower;  it  then  turned  right  side  up  with  the  front  legs  on  the  remaining 
part  of  the  lower  lip.     This  gave  it  a  sufficient  foothold  for  gathering  nectar. 

Lips  removed  except  lower  lobe. — The  median  lobe  thus  left  formed 
a  landing-platform,  so  that  Osmia  phaceliae  was  able  to  obtain  nectar  in 
the  usual  fashion. 

Corolla  tube  shortened  half. — Clisodon  terminalis  poised  in  the  air 
before  these  flowers,  but  did  not  land.  Melissodes  fremonti,  Osmia  phaceliae, 
and  Andrena  vicina  entered  them  and  obtained  nectar.  Some  individuals 
of  Pseudomasaris  vespoides  landed,  but  could  not  hang  on  and  suck  nectar, 
as  too  little  of  the  corolla  was  left  to  serve  as  a  platform  for  them. 

Petals  separated. — When  the  petals  are  separated  to  the  base,  they 
are  long,  slender,  and  recurved,  since  they  lack  mutual  support.  The 
stamens  consequently  spread  out  in  all  directions.  Osmia  phaceliae  went 
directly  to  the  nectar,  instead  of  first  standing  at  the  corolla  mouth  and 
rubbing  its  thorax,  as  in  the  normal  flower. 

Lower  lip  split  into  three  petals. — Osmia  bruneri  stood  on  the  middle 
petal  and  continued  to  suck  nectar,  in  spite  of  the  fact  that  its  weight 
caused  this  to  bend  down  vertically.  It  did  not  come  in  contact  with  the 
anthers  and  style  at  all  in  these  flowers. 


72 


NORMAL  AND  EXPERIMENTAL  POLLINATION. 


A  second  corolla  slipped  over  the  staminode. — This  gives  the  flower 
an  unusual  appearance,  as  though  it  were  doubled,  and  interferes  with 
entrance  to  the  corolla.  Osmia  melanotricha  and  0.  pentstemonis  landed 
and  tried  to  enter,  but  failed. 

Comparative  relations. — An  experiment  in  which  normal,  mutilated, 
and  inverted  flowers  were  placed  in  the  same  group  was  devised  to  determine 
the  effect  of  competition.  Three  spikes  of  each  type  of  mutilation  and  an 
inverted  one  were  used  with  11  normal  spikes  for  comparison.  Table  51 
shows  the  results. 


Table  51. — Inverted  and  mutilated  flowers. 


Species. 

Normal. 

Inverted. 

Style 
removed. 

Corolla 
removed. 

Corolla 
2-divided. 

51 

1 

28 

19 

18 

0 

1 

9 
0 
3 
4 

1 
3 
2 

2 
0 
1 
0 
0 
0 
0 

2 
0 
0 
1 
0 
1 
0 

2 
0 
0 
1 
0 
0 
0 

Apis  mellifica 

Pseudomasaris  vespoides. .  . 

Melissodes  fremonti 

Prosopis  varifrons 

Total 

118 

22 

3 

4 

3 

ARTIFICIAL  AND  PAINTED  FLOWERS. 

The  flowers  of  this  species  are  bright  blue  in  color  and  stand  out  conspic- 
uously against  the  buff  of  the  gravel-slides  on  which  they  grow.  The 
racemes  are  6  to  12  inches  long  and  each  plant  has  several,  so  that  the  color 
mass  is  large  and  conspicuous  from  some  distance. 

Crepe-paper  corollas. — The  corollas  of  half  the  flowers  of  4  racemes  (25 
flowers)  were  removed  and  replaced  by  tubular  paper  corollas  in  red,  blue, 
green,  white,  or  yellow.  Although  the  normal  flowers  were  visited  as  usual 
during  the  morning,  no  insects  even  attempted  to  enter  the  artificial  ones. 

Corolla  painted  with  water-colors. — Half  of  the  flowers  on  5  racemes 
were  painted  red,  yellow,  or  green.  One  Vespa  germanica  passed  by  red  and 
yellow  to  work  on  the  normal  ones  adjacent.  Another  Vespa  observed 
went  to  2  flowers  painted  yellow,  but  passed  by  the  neighboring  red  ones. 
Clisodon  terminalis  entered  the  normal  flowers,  but  ignored  the  painted  ones. 
Osmia  pentstemonis  was  less  discriminating  and  different  individuals  visited 
the  yellow  flowers  repeatedly.  They  flew  from  yellow  to  normal  flowers 
and  then  to  red  ones,  etc.,  as  they  found  the  flowers  in  a  convenient  order, 
but  they  avoided  the  green  ones  to  some  extent.  One  individual  inspected 
the  green,  but  passed  to  work  at  yellow  and  red,  and  then  returned  to  the 
green.  It  next  went  to  yellow,  to  red,  to  a  normal  flower,  and  then  back  to 
red. 

HONEY  AND  ODOR. 

Sirup  added. — Diluted  Karo  sirup  was  placed  in  various  positions  on  the 
flower.     One  individual  of  Osmia  pentstemonis  entered  blossoms  with  a  drop 


PENTSTEMON   GRACILIS.  73 

of  diluted  Karo  on  the  anthers  without  noticing  its  presence,  and  went 
directly  to  the  anthers  as  usual.  Another  twice  visited  a  flower  with  a 
drop  at  the  right  corner  of  the  corolla  mouth,  and  rubbed  the  anthers  without 
discovering  the  sirup.  Halictus  pulzenus  entered  flowers  with  Karo  on  the 
anthers  as  it  did  normal  ones,  that  is,  upside  down.  It  walked  through 
one  drop,  turned  around,  and  sipped  it  up  before  flying  away.  Vespa 
germanica  visited  every  flower  on  the  stalk  except  those  with  the  Karo 
drop.  Osmia  melanotricha  entered  a  flower  with  Karo  at  the  right  corner 
of  the  mouth,  straddling  the  staminode  in  the  usual  manner,  but  before 
reaching  the  nectar  turned  around  and  came  out  at  the  left  corner. 
Bombus  juxtus  almost  entered  such  a  flower,  but  suddenly  flew  to  the  next 
one. 

PENTSTEMON  GRACILIS. 

NORMAL  POLLINATION. 

Habit  and  structure. — This  is  the  smallest  flowered  species  of  Pent- 
stemon  found  in  the  Pike's  Peak  region.  The  corolla-tube  is  narrow  and 
comparatively  long,  1  to  2  cm.,  and  the  limb  extends  at  right  angles  to  the 
tubular  portion.  The  racemes  are  erect,  the  color  varying  from  delicate 
pink  to  pale  blue.  It  grows  on  warm  slopes  and  blooms  earlier  than  the 
other  species  in  the  locality,  and  is  sought  particularly  by  various  species 
of  Osmia. 

Behavior. — Osmia  bruneri  and  pentstemonis  push  the  head  into  the 
corolla-tube,  the  anthers  and  stigma  rubbing  against  the  hairs  on  the 
dorsal  surface  of  the  thorax  as  the  bee  sucks  nectar.  0.  phaceliae  rests 
on  the  lower  lip,  and  then  enters  the  flower  in  a  normal  position.  Its 
hind  legs  hang  over  the  lip  and  the  front  pair  rest  in  the  corolla-tube. 
It  goes  from  one  flower  stalk  to  the  next  and  enters  flowers  at  about  the 
same  level,  in  preference  to  visiting  all  the  open  flowers  on  one  stalk.  The 
same  flower  is  visited  repeatedly  by  different  individuals  and  sometimes 
one  bee  returns  several  times.  Prosopis  elliptica  enters  in  the  normal 
position  and  turns  so  that  it  either  stands  upside  down  or  sidewise  within 
the  corolla  while  collecting  pollen.  Halictus  (Chloralidus)  sp.  lands  on 
the  lower  lip  in  the  normal  position,  and  then  turns  upside  down,  hanging 
suspended  from  the  upper  lip.  The  tip  of  the  abdomen  touches  the  outer 
pair  of  anthers  as  it  scrapes  pollen  on  to  the  hind  legs. 

Bombus  juxtus  lands,  thrusts  its  head  in  and  places  its  front  legs  around 
the  two  outer  lobes  of  the  lower  lip  as  it  sips,  the  hairs  on  its  head  rubbing 
against  the  stigma  meanwhile.  It  enters  the  flower  upside  down  as  well 
as  in  the  normal  position.  This  bee  visited  pink  and  blue  flowers  without 
discriminating  between  the  two.  In  one  plant  with  unusually  small  flowers, 
it  could  not  get  its  head  into  the  corolla-tube.  However,  it  inspected 
these  and  tried  to  enter,  even  splitting  the  corolla-tube  in  the  attempt. 
B.  juxtus  did  not  accumulate  the  heavy  pollen  loads  exhibited  by  B.  bifarius. 
The  latter  pushes  its  ligule  into  the  flowers  for  nectar,  the  recurved  part 
of  the  lobes  extending  past  the  thorax  to  the  base  of  the  abdomen.  As  it 
sips,  the  anthers  rub  against  the  dorsal  side  of  the  thorax.  Most  of  the 
individuals  carried  heavy  pollen  loads  on  their  legs,  but  they  were  not  col- 


74 


NORMAL  AND  EXPERIMENTAL  POLLINATION. 


lecting  pollen  at  the  time.  As  B.  bifarius  leaves  the  flower,  it  scrapes 
pollen  from  the  dorsal  surface  of  its  thorax  with  its  front  legs  and  places  it 
on  the  hind  ones.  One  individual  started  to  suck  nectar  in  the  normal 
position,  and  then  turned  upside  down  and  scraped  pollen.  Another 
individual  behaved  in  the  same  manner  on  one  flower  and  then  visited  the 
next  flower  in  the  normal  way.  The  third  landed,  at  once  turned  upside 
down,  and  commenced  scraping  pollen,  working  in  the  same  fashion 
on  three  flowers  in  succession.  The  assumption  of  the  normal  or  inverted 
position  by  B.  bifarius  apparently  depended  on  whether  it  came  for  nectar 
or  pollen. 

Apis  mellifica  is  so  large  that  only  its  head  and  half  of  its  thorax  can 
enter  the  corolla-tube.  These  parts  are  hairy,  and  after  sucking  nectar 
the  bee  comes  out  dusted  with  pollen.  Titusella  pronitens  stands  with  its 
hind  legs  on  the  lower  recurved  petals  and  the  front  ones  on  the  corolla- 
tube,  while  it  pushes  out  its  ligule  and  takes  nectar.  Anthophora  simillima 
inspects  these  flowers,  but  none  land.  Systoechus  vulgaris  has  a  tongue  as 
long  as  the  corolla-tube,  so  long  indeed  that  the  head  usually  does  not  touch 
the  anthers  or  stigma  in  sucking  nectar.  If  pollination  is  accomplished 
by  this  fly,  it  is  done  by  the  ligule  as  it  enters  and  leaves  the  corolla.  Selas- 
phorus  platycercus  is  a  very  persistent  visitor.  In  the  course  of  a  morning's 
observation  the  same  bird  sucked  nectar  once  or  twice  from  every  open 
flower  on  the  whole  slope.  This  species  worked  so  rapidly  from  flower  to 
flower  that  even  when  there  were  only  one  or  two  visitors  every  flower 
in  the  locality  was  reached. 


Table  52.- 

-Visitors  to  normal  flowers. 

Species. 

Observations. 

1 

2 

3 

4 

5 

6 

1 

7 
12 
0 
0 
7 
2 
0 
1 
1 
0 
0 
4 

0 
15 
2 
0 
1 
0 
1 
1 
1 
1 
1 
3 
1 

15 
5 
0 
3 
0 
0 

1 

0 
0 
0 
0 
0 
0 

1 
12 

0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 

0 
13 
1 
0 
0 
14 
0 
0 
0 
0 
0 
0 
0 

1 
20 
6 
0 
0 
10 
2 
0 
0 
1 
0 
0 
0 

Pseudomasaris  vespoides 

Halictus  (Lasioglossum)  sp 

(Chloralictus)  sp 

Total 

Relative  total 

35 

9 

27 
2 

24 
24 

13 
13 

28 
19 

40 
26 

Calendars. — The  normal  visitors  to  this  species  as  observed  during  an 
hour  period  on  six  different  days  are  grouped  in  table  52.  The  first  list 
was  made  at  the  entrance  to  Englemann  Canyon  on  June  13,  when  the 
plants  were  past  their  prime  and  212  open  flowers  on  30  spikes  were  in  the 
group.     The  second  list  was  made  on  82  spikes,  bearing  526  open  flowers, 


PENTSTEMON   GRACILIS.  75 

found  at  Long's  Ranch  on  the  Ute  Trail  on  June  19.  The  last  four  lists 
were  made  in  the  vicinity  of  the  Alpine  Laboratory;  50  flowers  were  under 
observation  on  the  first  two  days,  June  15  and  16;  85  open  flowers  on  169 
spikes  on  the  third,  June  17;  and  72  flowers  on  175  spikes  on  the  fourth, 
June  18. 

EXPERIMENTS. 

CHANGE  OF  POSITION. 

Racemes  inverted. — Bombus  juxtus  entered  the  inverted  flowers  as  if 
it  did  not  notice  the  difference.  It  stayed  in  the  corolla  for  a  shorter  time 
than  with  normal  flowers  and  probably  did  not  find  the  nectar.  Osmia 
phaceliae  pushed  into  the  corolla,  thrust  out  its  ligule,  and,  not  finding  the 
opening  to  the  nectary,  went  to  the  next  flower.  It  also  failed  to  obtain 
nectar  here  and  then  visited  a  third  flower  that  was  in  the  normal  position. 
The  hairy  thorax  rubbed  the  mature  pair  of  anthers,  regardless  of  whether 
this  was  the  front  or  rear  pair.  It  also  visited  flowers  with  the  pollen 
practically  shed,  the  deflexed  stigma  scraping  the  thorax  as  the  bee  sipped 
nectar.  0.  pentstemonis  ate  the  pollen  that  had  fallen  on  the  floor  of 
the  corolla,  as  also  that  on  the  staminode  and  anthers.  Prosopis  varifrons 
turned  upside  down  in  order  to  gain  entrance  to  the  flowers. 

Racenie  horizontal. — Bombus  juxtus  turned  to  take  a  horizontal 
position  and  entered  at  once  in  the  usual  relation  to  the  parts. 

MUTILATION. 

Landing-platform  removed. — The  lower  lip  of  the  corolla  was  removed 
to  destroy  the  landing-platform  and  in  consequence  Bombus  and  Apis  were 
not  able  to  enter  such  flowers.  Osmia  phaceliae  did  not  need  the  lower  lip 
for  support,  but  straddled  the  staminode  in  such  a  position  as  to  take  nectar. 

Brush  of  staminode  removed. — There  was  no  difference  in  the  behavior 
of  the  visitors  to  these  flowers. 

Anthers  and  recurved  portion  of  upper  lip  removed.— Halictus 
pulzenus  entered  the  flowers  upside  down  in  the  usual  way  and  rubbed  the 
upper  surface  of  its  body  against  the  filaments,  as  if  noting  no  change. 

Upper  lip  partly  removed. — This  exposes  the  anthers  to  full  view,  but 
leaves  the  lower  lip  unchanged  as  a  landing-platform.  It  also  gives  the 
observer  a  much  better  opportunity  to  view  the  interior  of  the  flower  while 
the  bee  is  securing  nectar.  As  Clisodon  terminalis  sucks  nectar,  it  moves 
its  head  back  and  forth  once  or  twice  and  the  upper  parts  become  covered 
with  pollen,  which  is  then  removed  by  the  stigma  in  older  flowers.  In  the 
case  of  Bombus  juxtus,  the  first  pair  of  anthers  rub  the  top  of  the  abdomen 
and  the  second  the  top  of  the  thorax,  but  only  when  mature.  In  these 
flowers  the  bee  did  not  go  to  the  exposed  nectary  directly,  but  always  passed 
under  the  arch  made  by  the  stamens  and  style,  as  is  its  custom  in  normal 
flowers.  When  the  style  is  mature,  it  is  in  position  to  touch  the  back  of  the 
abdomen. 

Lobes  of  upper  lip  separated. — Osmia  phaceliae  goes  into  these  flowers 
apparently  without  noticing  any  difference,   the  whole  procedure  being 


76  NORMAL  AND  EXPERIMENTAL  POLLINATION. 

exposed  to  view.     As  the  bee  sucks  nectar,  the  hairs  of  the  thorax  are 
brushed  against  the  anthers  or  the  stigma. 

Petals  split  to  the  base. — Osmia  phaceliae  usually  stands  on  the  lower 
lip,  and  a  single  petal  suffices  to  support  it  when  the  lobes  are  split.  0. 
bruneri,  on  the  contrary,  is  so  heavy  that  a  single  petal  will  not  support  its 
weight,  and  hence  it  was  unable  to  obtain  a  foothold.  Bombus  juxtus 
had  even  greater  difficulty  in  landing  because  of  its  weight.  It  finally 
found  a  position  in  which  it  was  supported  by  the  two  outer  petals.  It 
then  felt  around  with  its  ligule  until  it  found  the  arch  under  the  stamens  and 
went  to  the  nectar  in  the  usual  manner.  Vespa  germanica  entered  these 
flowers,  but  stayed  only  a  very  short  time,  acting  as  though  uneasy  because 
of  the  unsteady  foothold. 

PENTSTEMON  GLAUCUS. 
NORMAL  POLLINATION. 
Normal  behavior. — Thanaos  martialis  lands  on  the  lower  lip  of  the 
corolla,  where  it  feels  around  with  its  ligule  until  it  finds  the  nectar,  the 
anthers  and  stigma  rubbing  against  the  hairs  of  its  back  meanwhile. 
Bombus  proximus  and  edwardsi  enter  the  flowers  by  landing  on  the  lower 
lip  and  going  directly  to  the  nectary.  One  bee  tried  to  turn  around  and 
enter  a  half-open  bud  upside  down,  but  was  not  successful.  Osmia  pent- 
stemonis  works  on  the  anthers  upside  down,  so  that  the  ventral  scopa  rubs 
them.  It  comes  out  of  the  normal  flower  head  first  and,  as  it  starts  to  fly, 
the  back  of  its  head  comes  in  contact  with  the  anthers  or  stigma  tip. 

EXPERIMENTS. 

MUTILATED. 

Upper  lobes  split  to  base. — Osmia  pentstemonis,  after  trying  to  land 
on  the  projecting  staminode,  placed  its  front  legs  on  the  outer  lobes  of  the 
lower  lip  and  the  others  on  the  middle  lobe  and  worked  easily,  reaching 
the  nectar  readily.  The  corolla  mouth  is  so  large  that  the  bee  does  not 
usually  come  in  contact  with  the  anthers  and  the  stigma.  Its  scopa  rubs 
the  hairs  of  the  staminode,  but  pollination  is  not  often  effected  by  this 
visitor.  Bombus  morrisoni  landed  on  some  of  the  flowers,  but  flew  away 
at  once,  while  in  other  cases  it  inspected  them  without  landing. 

Lower  lip  removed. — Osmia  pentstemonis  had  difficulty  in  landing, 
slipping  back  and  forth  and  its  head  rubbing  the  anthers. 

Outer  lobes  of  lower  lip  removed. — Thanaos  martialis  normally 
places  the  front  pair  of  legs  on  the  outer  lobes  and  the  weight  of  its  body  on 
the  middle  one.  With  the  outer  lobes  removed  it  finally  succeeded  in  landing 
by  putting  its  front  legs  at  the  edges  of  the  middle  lobe  and  the  weight  of  its 
body  on  a  bud  under  the  flower. 

Staminode  removed. — Bombus  juxtus  landed,  then  moved  from  side 
to  side,  and  backed  out.  It  started  into  the  flower  again,  stopped,  and 
went  directly  to  the  nectar.  In  normal  flowers  it  follows  the  staminode  to 
the  nectar  at  once. 


PENTSTEMON    SECUNDIFLORUS. 


77 


Middle  lobe  of  the  lower  lip  removed. — Bombus  morrisoni  went  into 
3  flowers  of  this  type,  apparently  without  noting  any  change,  and  B.  juxtus 
behaved  similarly. 

Upper  lip  removed. — Bombus  morrisoni  noted  no  change. 

PENTSTEMON  SECUNDIFLORUS. 
NORMAL  POLLINATION. 
Behavior. — Bombus  proximus  alights  on  the  lower  lip  of  the  corolla 
and  then  turns  around  on  to  the  upper  lip,  standing  upside  down  while 
working.  It  flies  from  one  open  flower  to  another  in  a  cluster  and  then 
to  the  next  cluster.  Vespa  germanica  stands  on  the  lower  lip  and  pushes 
its  head  far  into  the  flower  for  nectar.  It  transfers  the  pollen  collected  on 
the  head  to  its  hind  legs  with  the  front  ones.  After  visiting  many  flowers, 
it  rests  on  the  ground  before  going  to  others. 

Calendar. — A  calendar  is  given  below  of  visits  during  a  42-minute  period 
to  24  spikes  bearing  125  open  flowers.  Holes  had  been  bored  by  robbers 
at  the  base  of  the  corolla  on  the  upper  side  of  many  of  these  flowers.  Pseudo- 
masaris  vespoides  went  to  many  flowers  twice,  collecting  in  the  usual  way 
from  those  previously  robbed  by  some  other  insect.  Anthophora  simillima 
stopped  at  only  2  or  3  flowers  at  a  time  and  was  easily  frightened.  Sys- 
toechus  vulgaris  was  a  persistent  visitor,  going  to  as  many  as  59  flowers  in 
rapid  succession. 

Calendar  1. — Visits  to  normal  flowers. 


llh06m  Anthophora  simillima,  1. 

11  10  Osmia  melanotricha,  1;  Prosopis 
wootoni,  1 ;  Pseudomasaris  ves- 
poides, 15. 

11  13     Anthophora,  1. 

11  15     Anthophora,  2. 

11  16     Bombus  juxtus,  1. 


llh20m  Osmia,  1. 

11  21  Bombus,  1;  Systoechus  vulgaris,  59. 

11  27  Anthophora,  5;  Megachile  wootoni,  c 

11  30  Anthophora,  1. 

11  34  Osmia  pent3temonis,  4. 

11  45  Andrena,  1. 

11  48  Monumetha  albifrons,  1. 


The  variety  of  visitors  to  this  species  is  shown  by  table  53,  column  1 
giving  the  visitors  during  a  40-minute  period  and  column  2  during  48 
minutes. 

Table  53. — Visitors  to  normal  flowers. 


Species. 

1 

2 

Species. 

1 

2 

Systoechus  vulgaris 

Andrena  madronitens 

Anthophora  simillima 

7 
6 
0 
0 
0 
0 

1 

1 

1 
4 
1 
1 

2 

1 

1 
0 
0 

1 
1 

2 
1 

1 
0 
0 

Pseudomasaris  vespoides .  .  . 

Monumetha  albifrons 

Osmia  melanotricha 

pentstemonis 

Selasphorus  platycercus .... 
Total : 

..17 

15 

EXPERIMENTS. 

ODOR. 

Powders   and   extract. — Flowers   were   sprinkled   with  four  kinds   of 
talcum  powder.     Many  individuals  of  Bombus  juxtus  landed  on  such  flowers, 


78 


NORMAL  AND  EXPERIMENTAL  POLLINATION. 


but  flew  away  immediately.  Between  such  visits  they  stopped  at  normal 
flowers  and  sipped  nectar.  Halictus  pulzenus  behaved  in  a  similar  manner. 
Flowers  sprinkled  with  talcum  one  day  lost  their  odor  during  the  night  and 
the  following  day  were  visited  normally  by  both  Bombus  juxtas  and  Halictus 
pulzenus  for  nectar. 

Cotton-wads  sprinkled  with  peppermint  or  almond  essence  were 
placed  below  the  calyxes  of  28  mature  flowers,  and  28  noimal  ones  were 
left  for  comparison,  with  the  results  shown  in  table  54. 

Table  54. — Visitors  to  normal  and  scented  flowers. 


Species. 


Normal 
flowers. 


lint 


Peppermint  Almond 

scented.  scented. 


Bombus  juxtus 

bifarius 

proximus. . .  . 

Prosopis  basalis 

Andrena  madronitens 
Osmia  bruneri 

Total 


8:38 

6:27 

0:0 

3:4 

1:1 

1:1 


5:5 
0:0 
1:1 
0:0 
0:0 
0:0 


19:71 


0:0 
0:0 
0:0 
0:0 
0:0 
0:0 


SUMMARY. 

Practically  all  visitors  solved  successfully  the  problems  involved  in 
changes  of  position,  inverted  flowers  being  visited  as  much  as  normal  ones 
at  least.  On  the  other  hand,  a  light  plug  of  cotton  rendered  all  visits 
unsuccessful.  When  the  styles,  stamens,  and  staminode  were  removed 
in  Pentstemon  glaber,  most  of  the  visitors  left  without  securing  nectar,  while 
in  the  case  of  P.  glaucus  with  the  staminode  excised,  Bombus  juxtus  entered, 
backed  out,  and  then  went  in  again  to  the  nectar.  When  the  lips  were 
separated  in  P.  glaber,  about  half  the  visitors  flew  away  as  if  disturbed. 
With  the  lobes  split  to  the  base,  landing  was  modified  to  a  marked  degree, 
but  it  became  impossible  only  in  the  case  of  one  or  two  species.  The 
removal  of  the  upper  lip  produced  no  effect,  but  with  the  lower  lip  shortened 
or  removed,  the  larger  bees,  such  as  Bombus  and  Apis,  were  unable  to  land 
on  the  small  flowers  of  P.  gracilis,  while  Osmia  was  obliged  to  make  use  of 
the  staminode  for  landing.  Splitting  the  upper  lobes  to  the  base  in  P. 
gracilis  caused  Bombus  to  inspect  merely  or  to  fly  away  without  securing 
nectar,  while  splitting  the  lower  ones  in  P.  glaber  caused  difficulty  in  alighting 
even  to  smaller  bees  such  as  Osmia.  When  the  interior  of  the  flower  was 
disarranged  by  slipping  a  corolla  over  the  staminode,  Osmia  failed  to  find 
an  entrance. 

Artificial  flowers  of  P.  glaber  secured  no  visitors  whatever,  but  natural 
flowers  painted  with  water-colors  were  well  visited.  The  addition  of  honey 
had  practically  no  effect,  while  essences  greatly  reduced  the  visits  to  P. 
secundifiorus.  Flowers  scented  with  peppermint  received  one-third  as 
many  visitors  and  one-twelfth  as  many  visits  as  the  normal  ones.  Those 
scented  with  almond  were  completely  shunned,  in  marked  contrast  with  the 
behavior  in  Chamaenerium. 


MONARDA   FISTULOSA.  79 

MONARDA  FISTULOSA. 

NORMAL  POLLINATION. 

Habit  and  structure. — This  species  grows  in  fairly  dense  groups  on 
warm  half-gravel  slides,  the  numerous  stems  of  each  plant  making  a  brilliant 
mass  of  color.  This  attractiveness  is  due  in  large  measure  to  the  capitate 
clusters  of  bright  pink-purple  flowers.  The  latter  are  erect  or  ascending, 
and  consist  of  a  slender  tube  with  two  long  lips.  The  upper  lip  is  subulate 
and  protects  the  anthers  and  stigmas  when  young,  while  the  lower  is  strap- 
shaped  and  forms  a  landing-platform.  The  anthers  are  reduced  to  two, 
and  the  nectar  is  abundant,  so  that  the  flowers  are  visited  almost  wholly 
for  nectar.  Since  the  flowers  bloom  late  in  the  summer,  they  constitute 
the  chief  attraction  to  the  butterflies  and  larger  bees  at  this  time  (plates 
13  and  16). 

Behavior. — Bombus  juxtus  lands  on  the  lower  lip  of  the  corolla  and 
sucks  nectar  through  the  tube,  pollinating  the  flower  as  its  head  rubs  against 
the  anthers  or  stigma.  One  B.  juxtus  was  observed  stealing  nectar  from 
the  base  of  the  corolla-tube,  but  this  was  not  the  normal  procedure  for  the 
species.  B.  bifarius,  proxirnus,  and  pennsylvanicus  robbed  Monarda  through 
holes  at  the  base  of  the  tube  during  several  seasons  in  succession,  but  in 
1922  all  the  individuals  observed  secured  nectar  in  the  normal  way.  The 
year  previous  Bombus  proxirnus  was  observed  puncturing  the  corollas  in 
one  group  without  making  a  single  normal  visit,  while  in  a  second  group  a 
few  yards  away  it  just  as  regularly  obtained  nectar  in  the  proper  manner. 
Andrena  crataegi  is  unable  to  make  holes  easily  in  the  corolla-tube  and  con- 
sequently takes  advantage  of  those  made  by  other  species.  Prosopis 
elliptica  stands  on  the  lower  lip  of  the  corolla  and  eats  the  pollen  fallen  from 
the  stamens.  Halictus  pulzenus  alights,  walks  around  on  the  anthers, 
and  then  goes  down  the  filaments  to  the  nectary.  It  gathers  pollen  from 
the  anthers,  but  it  does  not  come  in  contact  with  the  stigma,  except  by 
accident. 

Erynnis  leonardus  snowi  alights  on  the  corolla  lip,  unrolls  its  ligule,  and  tries 
to  find  the  nectar.  The  ligule  often  slips  along  the  outside  of  the  tube,  and 
even  when  it  starts  down  the  tube  it  is  withdrawn  occasionally  as  if  the 
butterfly  were  uncertain.  The  latter  does  not  have  very  good  control  of  the 
ligule  and  its  eyes  are  apparently  so  placed  that  it  can  not  see  down  the  tube 
to  guide  this  by  sight.  The  difficulty  experienced  by  Erynnis  is  probably 
due  to  its  landing  at  the  margin  of  the  head.  This  is  indicated  by  the  fact 
that  Argynnis  atlantis  regularly  alights  in  the  center,  the  angle  of  the  ligule 
approaching  that  of  the  corolla-tube  and  thus  rendering  the  insertion  of 
the  ligule  much  easier.  The  control  of  the  larger  butterfly  is  perhaps 
greater  also,  as  it  has  little  difficulty  in  inserting  the  tongue  in  shortened 
corollas  on  the  first  trial.  As  a  consequence,  this  species  works  on  Monarda 
with  something  of  the  rapidity  of  Bombus.  Selasphorus  platycercus  is  a 
frequent  visitor  to  these  flowers,  where  it  poises  in  the  air  in  front  of  the 
flower-head  and  works  very  rapidly.  It  pushes  its  bill  into  every  flower 
and  is  a  very  effective  pollinator.  The  fluttering  motion  rubs  the  bill  and 
feathers  on  the  front  of  the  head  against  the  stigma  and  also  collects  pollen 
from  the  anthers. 


80 


NORMAL  AND  EXPERIMENTAL  POLLINATION. 


The  visitors  to  normal  flowers  as  observed  for  an  hour  on  July  5  and  8 
are  given  in  table  55.  There  were  50  Monarda  heads  used  on  the  first  date 
and  80  on  the  second. 

Table  55. — Visitors  and  visits  to  normal  flowers. 


Species. 

July  5. 

July  8. 

35:35 

13:13 

0:0 

25:25 

16:16 

9:9 

2:2 

0:0 

0:0 

2:2 

40:70 
6:6 
1:1 
0:0 
3:6 
0:0 
0:0 
5:24 
1:3 
0:0 

Bombus  proximus 

morrisoni 

Clisodon  terminalia 

wootoni 

Total 

102:102 

56:110 

As  would  be  expected  from  the  form  of  the  flower,  more  than  half  the 
visitors  belonged  to  the  two  genera  of  butterflies,  Erynnis  and  Argynnis. 
While  all  four  species  of  Bombus  are  able  to  secure  nectar  in  the  proper  way, 
this  is  sufficiently  difficult  so  that  they  often  avoid  Monarda  when  Geranium 
or  Aster  are  near,  or  they  steal  the  nectar  by  puncturing  the  corolla  at  the 
base,  as  was  done  by  all  the  visiting  individuals  of  Bombus  proximus  and 
morrisoni  in  the  present  observations. 

Meehan  (1892:449)  found  that  the  anthers  of  Monarda  fistulosa  burst  as 
the  lips  expand  and  while  the  stigma  is  still  infolded  by  the  curved  portion 
of  the  upper  lip.  By  nightfall  of  the  second  day  the  stamens  begin  to  wither, 
the  upper  anther-cell  shriveling  first.  In  the  morning  the  styles  grow  out 
beyond  the  upper  lip  and  the  stigmas  separate.  Keller  (1892 :  452)  observed 
that  the  anthers  shed  their  pollen  and  the  stigmas  diverge  widely  in  the 
closed  buds,  but  this  was  probably  a  case  of  cleistogamy  due  to  cold,  as 
the  observations  were  made  in  November.  Longyear's  observations  (1909: 
84)  are  in  accord  with  those  of  Meehan,  as  is  the  detailed  life-history  (plate 
13,  figs.  11  to  16). 

EXPERIMENTS. 

MUTILATION  AND  COMPETITION. 
Plan. — In  order  to  permit  a  wider  range  of  selection,  mutilation  and 
competition  experiments  were  combined  in  the  case  of  Monarda.  The 
flowers  of  this  plant  lend  themselves  with  especial  readiness  to  studies  of 
the  effect  of  mutilation,  owing  to  the  pronounced  zygomorphy.  Moreover, 
the  arrangement  of  the  flowers  in  heads  affords  an  opportunity  to  vary  the 
kind  of  competition.  Paper  disks  and  paper  composite  flowers  were  also 
employed  in  some  of  the  series.  In  order  to  determine  in  some  degree  the 
effect  of  place  and  time,  two  observers  were  employed  to  record  the  behavior 
in  two  separate  clumps,  distant  1  to  3  meters  from  each  other,  and  the 
calendars  were  repeated  a  week  apart  and  on  two  successive  days.  In 
consequence  of  the  closing  of  the  flowering  period  for  many  plants,  the 


MONARDA   FISTULOSA. 


81 


number  of  species  and  individuals  visiting  Monarda  was  large,  comprising 
representatives  of  the  three  great  groups.  For  the  sake  of  brevity  the  clue 
name  alone  is  given  in  the  calendars,  and  the  species  are  listed  here: 


Hymenoptera: 

Andrena  madronitens 
Apis  mellifica 
Bombus  appositus 
bifariua 
edwardsi 
hunti 
juxtus 
morrisoni 
occidentalis 


Hymenoptera — continued. 
Clisodon  terminalis 
Colletes  sp. 
Halictus  lasioglossum 

puJzenua 
Monumetha  albifrons 
Prosopis  varifrons 


Diptera: 

Anthrax  nigra 

Aristatus  montanus 

Eristalis  arbustorum 

Syrphus  americanus 
Lepidoptera: 

Argynnis  atlantis 

Atrytone  taxile3 

Chrysophanus  sirius 

Erynnis  leonardus  snowi 

Gnophaela  vermiculata 

In  these  more  complicated  calendars  it  seems  desirable  to  use  "normal" 
for  such  flowers,  the  number  then  indicating  the  number  of  flowers  visited 
in  each  head.  Visits  were  for  nectar,  unless  otherwise  indicated,  but  in  the 
case  of  Clisodon,  p.  and  n.  are  employed  to  denote  those  for  pollen  or  nectar 
respectively.  When  the  time  is  given  in  seconds  or  minutes,  it  applies  to 
all  the  visits  that  precede. 

First  series. — The  two  records  were  made  on  August  8  in  two  adjacent 
clumps  of  Monarda.  The  installation  consisted  of  approximately  the 
same  number  of  normal  and  modified  heads.  Crepe-paper  corollas  of  the 
size  of  those  of  Rubus  deliciosus  were  fastened  below  Monarda  heads,  making 
a  composite;  there  were  2  each  of  red,  yellow,  blue,  white,  and  green.     The 


Calendar  1. 


8h45m  Clisodon  upper  lip  off  4,  normal  6. 
8  47     Argynnis  lands  and  inspects  Chamae- 
nerium. 

Prosopis  Chamaenerium  2 

Clisodon  normal  2,  inspects  Chamae- 
nerium, normal,  1,  1,1,  corolla 
split  1,  normal  2,  corolla  shortened 
3n,  inspects  Chamaenerium. 

Bombus  occidentalis  Geranium  4,  in- 
spects crepe  Geranium. 

Prosopis  Chamaenerium  3. 

Argynnis  Chamaenerium  1,  normal  2. 

Bombus  bifarius  Geranium  5,  inspects 
crepe  Geranium. 

Argynnis  inspects  most  of  the  objects. 

Atrytone  normal  8,  2,  Chamaenerium 
2,  normal  3,  upper  lip  off  1,  Cham- 
aenerium   1,   normal  3,  rests   on 


8  48 
8  49 


8  51 

8  53 
8  55 

8  58 

9  00 
9  04 


9h07n 
9  11 


9  13 
9  14 


9  17 

9  22 
9  26 


yellow  composite,  but  does  not 

take  nectar. 
Atrytone  blue  composite  1,  upper  lip 

off  1. 
Argynnis  corolla  shortened  1,  normal 

1,  upper  lip  off  1. 
Argynnis  Geranium  2. 
B.  appositus  normal  3;  Atrytone  blue 

composite  4,  white  composite  3, 

normal  5,  Chamaenerium  3. 
B.   bifarius    Geranium  2;    Atrytone 

normal  3,  lower  lip  off  4,  rests  on 

normal,  normal  2. 
Erynnis  rests  on  yellow  composite; 

Clisodon  normal  3p,  upper  lip  off 

4n. 
Erynnis  normal  2. 


Calendar  2. 


9h29m  Atrytone,  blue  composite  1,  white 
composite  1,  normal  1. 

Atrytone,  lower  lip  off  1. 

Monumetha,  normal  2;  Syrphus,  nor- 
mal 1. 

Clisodon,  normal  4,  lower  lip  off  2p; 
inspects  both  yellow  composites 
and  normal  3. 

Gnophaela,  normal  4,  3;  Atrytone, 
normal  1,  red  composite  1. 


9  30 
9  31 


9  34 


9  37 


9h44m  B.  bifarius,  Geranium  2;  B.  occi- 
dentalis, Geranium  4,  inspects 
crepe  Geranium;  Clisodon,  nor- 
mal 7n,  lp;  B.  appositus,  normal 
4,  lower  lip  off  1. 

Clisodon,  normal  2p,  2n. 

B.  occidentalis,  Geranium  3;  Atrytone 
normal   2,    corolla   shortened   3. 

Atrytone,  lower  lip  off  3,  normal  3. 

Atrytone,  rests  on  yellow  composite. 


9  50 
9  51 


9  52 
9  55 


82 


NORMAL  AND  EXPERIMENTAL  POLLINATION. 


corollas  were  removed  from  2  heads  and  flowers  of  Chamaenerium  sub- 
stituted. Heads  were  also  mutilated  by  shortening  the  corolla  to  half  its 
length,  leaving  the  stamens  intact  in  one  case  and  removing  them  in  another, 

Table  56. — Summary  of  calendars. 
Calendar  1. 


Species. 

Norm. 
Mon. 

Upper 
Hp 
off. 

Lower 
lip 
off. 

Cor. 

short. 

Cor. 

short, 
stam. 

Cor. 
split. 

Mon. 
comp. 

Chamae. 
head. 

Norm. 
Ger. 

Crepe 
Ger. 

16 
3 
0 
0 
3 

26 
2 
0 

8 
0 
0 
0 

1 
2 
0 
0 

0 
0 
0 
0 
0 
4 
0 
0 

3 
0 
0 
0 

1 
0 
0 
0 

0 
0 
0 
0 
0 
0 
0 
0 

1 
0 
0 
0 
0 
0 
0 
0 

0 
0 
0 
0 
0 
5b:3w 
0 
0 

2i 

0 

0 

0 
l:li 
6 
0 
5 

0 
0 
7 
4 
2 
0 
0 
0 

0 

0 

li 

li 

0 

0 

0 

0 

Bombus  appositus.  . 

bifarius 

occidentalis 

Total 

50 

11 

4 

4 

0 

1 

5b:3w 

12:3i 

13 

2i 

Calendar  2. 

Clisodon 

Bombus  appositus. . 

bifarius 

occidentalis 

Monumetha 

16:3i 

4 
0 
0 
2 

1 
7 
7 

0 
0 
0 
0 
0 
0 
0 
0 

2 

1 
0 
0 
0 
0 
4 
0 

0 
0 
0 
0 
0 
0 
3 
0 

0 
0 
0 
0 
0 
0 
0 
0 

0 
0 
0 
0 
0 
0 
0 
0 

yi 

0 
0 
0 
0 
0 
bwr 
0 

0 
0 
0 
0 
0 
0 
0 
0 

0 
0 
2 
7 
0 
0 
0 
0 

0 

0 

0 

li 

0 

0 

0 

0 

Total 

Grand  total. . 

37:3i 

0 

7 

3 

0 

0 

bwr :  yi 

0 

9 

li 

87:3i 

11 

11 

7 

0 

1 

6b4w 
r:yi 

12:3  i 

22 

3i 

Table  57. — General  summary. 


Species. 

Normal. 

Muti- 
lated. 

Other 
flowers. 

Species. 

Normal . 

Muti- 
lated. 

Other 
flowers. 

16 
3 
0 
0 
3 

26 
2 
0 

12 
0 
0 
0 
2 
6 
0 
0 

0 
0 
7 
4 
3 
6 
0 
5 

16 
4 
0 
0 
2 
1 
7 
7 

2 
1 
0 
0 
0 
0 
7 
0 

0 
0 
2 
7 
0 
0 
0 
0 

Bombus  appositus.  .  .  . 

bifarius 

occidentalis. . . 

Bombus  appositus 

bifarius 

occidentalis .  .  . 

Total  

Total    .  . 

50 

20 

25 

37 

10 

9 

Grand  total 

87 

30 

34 

MONARDA   FISTULOSA. 


83 


by  removing  the  lower  lip  or  the  upper  one,  and  by  splitting  the  tube  for 
its  entire  length,  each  type  being  represented  by  2  heads.  The  corollas 
of  5  Geranium  flowers  were  replaced  by  crepe-paper  ones  representing  the 
colors  red,  yellow,  blue,  green,  and  white,  and  these  were  grouped  with 
5  normal  flowers. 

Second  series. — The  two  records  were  made  on  August  14  from  8h20m 
to  10h40m  a.  m.,  in  two  clumps  of  Monarda  3  meters  apart.  The  number 
of  normal  and  modified  Monarda  heads  and  normal  Geranium  flowers  was 
approximately  the  same.  Five  heads  were  mutilated  by  shortening  the 
corollas  of  one  to  half  the  normal  length,  by  removing  the  upper  lip  in  the 
second,  the  lower  lip  in  the  third,  upper  lip  and  stamens  in  the  fourth,  and 
both  lips  in  the  fifth.  The  flowers  of  one  head  and  half  of  those  of  another 
were  replaced  by  corollas  of  Gilia  aggregata,  while  flowers  of  Chamaenerium 
angustifolium  were  substituted  for  half  of  those  of  a  third  head.  In  addition, 
two  racemes  of  the  latter  species  were  inserted  in  bottles  of  water  and  placed 
in  the  clump. 

Calendar  1. 


8h20m 
8  22 
8  24 
8  26 

8  29 

8  38 
8  40 

8  42 
8  44 
8  45 
8  48 
8  53 

8  54 
8  55 
8  56 


8  57 
8  59 


9  00 
9  03 


9  14 

9  15 

9  19 


Erynnis,  normal  2. 

Erynnis,  normal  1,  7,  2,  1;  70  seconds. 

Clisodon,  normal  7,  1,  4,  14. 

Erynnis,  normal  3,  2;  Chamaenerium 
2,  9;  80  seconds. 

Erynnis,  normal  3;  60  seconds;  Gera- 
nium 2,  2,  1. 

Erynnis,  normal  3,  1,  4. 

Erynnis,  normal  4,  upper  lip  off  4; 
Clisodon,  normal  1. 

Bombus  juxtus,  Chamaenerium  1. 

Clisodon,  normal  4,  5. 

Erynnis,  normal  1,  2,  3,  3,  5. 

Bombus  morrisoni,  normal  8. 

Erynnis,  normal  2,  touched  Chamae- 
nerium. 

Clisodon,  normal  1,  5,  3,  2. 

Erynnis,  upper  lip  off  3. 

Erynnis,  visits  Chamaenerium  2,  but 
takes  no  nectar,  upper  lip  off  2, 
normal  2,  lights  on  leaf. 

Clisodon,  normal  6. 

Bombus  appositus,  3  to  4  flowers  each 
of  3  heads  (total  normal  10). 

Erynnis,  normal  3,  upper  lip  off  2,  leaf. 

Erynnis,  normal  2,  1,  1,  3;  55  seconds; 
upper  lip  and  stamens  off  4, 
upper  lip  off  5;  B.  juxtus,  normal 
5,  shortened  corolla  3,  both  lips 
off  1,  upper  lip  off  1. 

Erynnis,  upper  lip  off  12;  2  minutes; 
Geranium,  normal  2,  3;  30 
seconds.  Clisodon,  normal  8, 
10,  12,  10;  upper  lip  off  5;  40 
seconds;  normal  5,  40  seconds. 

Clisodon,  normal  6,  6,  inspected 
Chamaenerium. 

Erynnis,  normal  3,  Gilia  1,  Monarda, 
1  in  mixed  head,  tries  Chamae- 
nerium vainly. 

Erynnis,  Chamaenerium  3. 


9h21D 
9  23 
9  25 

9  30 


9  33 
9  35 


9  59 
10  04 


10  09 
10  13 


Erynnis,  Chamaenerium  2,  normal  2" 
Erynnis,  normal  2,  1,  Chamaenerium  1. 
Erynnis,  normal  4,  Chamaenerium  1, 

normal  5,  Gilia  2. 
Bombus  morrisoni,  normal  5;  Argyn- 

nis,     normal     12,     30     seconds; 

Chamaenerium  6,  20  seconds. 
Erynnis  merely  lands  on  2  horizontal 

Monarda. 
Erynnis,  normal  3,  Chamaenerium  2, 

both  lips  off  2,  upper  and  stamens 

off  9;  Clisodon,  normal  10,   12, 

3,  9,  5,  6. 

Clisodon,  normal  2,  3,  2,  4,  6,  7,  3,  5, 
8,  6,  1,  3. 

Bombus  appositus,  normal  6,  8,  5,  4, 
7,  8,  5,  8,  4,  4,  3,  8;  second 
individual  normal  4,  4,  upper  lip 
off  12,  2  minutes;  third  indi- 
vidual normal  8,  10,  12,  6 
Monarda  flowers  of  mixed  Gilia 
head,  normal  4,  8,  Chamaenerium 
8;  Clisodon  most  flowers  of  3 
heads  (total  normal  25),  all 
flowers  of  4  heads,  often  twice 
(total  normal  60),  5  heads  some 
twice  (total  normal  53),  6 
heads  (total  normal  58). 

Bombus   juxtus,    normal   2,    1,    5,    6, 

1,  3,  6,  5. 

Bombus  juxtus,  normal  6,  2,  1,  1,  1, 

2,  2,  2,  8,  1,  2,  10,  2,  upper  lip 
and  stamens  off  6,  then  goes 
vainly  to  shortened  corollas; 
second  individual   normal   3,   2. 

Bombus  appositus,  normal  3,  2,  2,  4, 

4,  1,  1,  2,  2,  2,  3,  9,  4,  2. 
Bombus    appositus,    both    lips    off    4, 

upper  lip  and  stamens  off  7, 
upper  lip  off  5,  normal  11,  6,  1, 
4,  1,  4,  5,  6;  1  minute. 


84 


NORMAL  AND  EXPERIMENTAL  POLLINATION. 


10h15m  Bombus  appositus,  normal  4;  Erynnis, 
normal  11;  2  minutes. 

10  20     Erynnis,  Gilia  2,  7,  2. 

10  23     Argynnis,  normal  1. 

10  25     Bombus  juxtus,  normal  3,  4. 

10  29  Bombus  appositus,  normal  5,  1,  1; 
Erynnis,  normal  8,  Chamae- 
nerium  1,  5. 

10  31     Bombus  juxtus,  normal  2,  6. 


Calendar  1 — Continued. 


10h32m  Clisodon,  upper  lip  and  stamens  off  6, 
normal  11,  5,  5,  Gilia  1,  normal 
9,  inspects  Chamaenerium,  nor- 
mal 4,  3,  4,  4,  15,  inspects 
Chamaenerium  and  Gilia,  nor- 
mal 6,  14,  thrice  (total  normal 
60),  shortened  corolla  1,  upper 
lip  and  stamens  off  3  vainly, 
upper  lip  off  3,  inspected  6  for 
pollen;  4  minutes  for  all. 


Calendar  2. 


9h10m  Bombus  juxtus,  Chamaenerium  1  in 
mixed  and  3  in  pure  head; 
Erynnis,  Monarda  2  in  mixed 
Chamaenerium  head. 

Erynnis,  lower  lip  off  1. 

Halictus  pulzenus,  normal  1. 

Halictus  pulzenus,  normal  1. 

Halictus  pulzenus,  normal  2;  Clisodon, 
upper  lip  off  3. 

Bombus  edwardsi,  normal  1. 

Bombus  appositus,  normal  1. 

Bombus  hunti,  9  normal  on  3  heads, 
Chamaenerium  10  normal  on 
3  racemes,  upper  lip  off  3  (total 
31),  normal  flowers  on  4  heads. 


9  23 
9  27 
9  29 
9  40 

9  50 
9  54 

9  58 


10h00m  Bombus  appositus,  26  normal  flowers 

on  5  heads;  Clisodon,  normal  9; 

B.  appositus  inspects  2  Geranium. 
10  20     Bombus  juxtus,  Geranium  5. 
10  24     Halictus  (Lasioglossum)  sp.   Geranium 

2;  Halictus  pulzenus,  Geranium  1. 
10  26     Bombus  juxtus,  normal  13,  Geranium 

15;  P.  varifrons,  Geranium  1. 
10  35     Bombus  occidentalis,  Geranium  14. 
10  36     Bombus  juxtus,  Geranium  2. 
10  41     Bombus  morrisoni,  Geranium  1. 


Table  58. — Summary  of  calendars. 
Calendar  1. 


.ft 

.ft 

ft 

8 

T3 

6 
3 

6  T3 

.  ® 

§  a 

3 

O 

Species. 

°*2 

ft«8 

o.  ° 

O    ° 

ft  m 

m 

& 

a 

.2 

.5 

a. a 
|  a 

a  1 

03    ? 

a 

s 

K% 

U 

h^l 

& 

PQ 

0 

O 

O 

o 

O 

£ 

621:6i 
220 

8 
17 

0 
0 

6:3i 
7 

0 
4 

i 

0 

0 
6Mon. 

1:11 

0 

0 
0 

2i 

8 

0 
0 

Bombus  appositus 

juxtus 

94 

1 

0 

40 

1 

3 

0 

0 

0 

1 

0 

morrisoni 

13 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

13 

100 

0 

28 

0 
0 

0 
13 

0 
2 

0 
0 

0 
1  Mon. 

0 
14 

0 
0 

6 
26:3i 

0 
10 

Total 

l,061:6i 

54 

0 

66:3i 

7 

4 

7  Mon. 

15:li 

0 

41:5i 

10 

Calendar  2. 

Clisodon 

9 

3 

0 

0 

0 

0 

0 

0 

0 

0 

0 

Bombus  appositus 

27 

0 

0 

0 

0 

0 

0 

0 

0 

0 

2i 

juxtus 

13 

0 

0 

0 

0 

0 

0 

0 

1 

3 

22 

edwardsi 

1 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

40 
0 

3 
0 

0 
0 

0 
0 

0 
0 

0 
0 

0 
0 

0 
0 

0 
0 

10 
0 

0 
14 

occidentalis 

morrisoni 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

1 

Halictus(Lasioglossum)sp 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

2 

pulzenus 

4 

0 

0 

0 

0 

0 

0 

0 

0 

0 

1 

Prosopis  varifrons  

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

1 

Erynnis 

Total 

0 

0 

1 

0 

0 

0 

0 

0 

2  Mon. 

0 

0 

94 

6 

1 

0 

0 

0 

0 

0 

1:2  Mon. 

13 

41:2i 

Grand  total ...... 

1,155 

60 

1 

66:3i 

7 

4 

7  Mon. 

15:li 

1:2  Mon. 

54:5i 

51:2i 

MONARDA   FISTULOSA. 

Table  59. — General  summary. 


85 


Species. 

Normal . 

Total 
muti- 
lated. 

Total 

other 

flowers. 

Species. 

Normal. 

Total 

muti- 
lated. 

Total 

other 

flowers. 

621 

220 

94 

13 

13 

100 

15 
28 
45 
0 
0 
43 

1 

8 
1 
0 
6 
50 

Bombus  edwardsi 

hunti 

occidentalis.  .  . 

morrisoni 

Halictus  (Lasioglossum) 

1 

40 

0 

0 

0 
4 
0 
0 

0 
3 
0 
0 

0 
0 
0 

1 

0 
10 
14 

1 

2 

1 
1 
0 

Bombus  appositus.  .  .  . 

juxtus 

morrisoni.  .  .  . 

Total 

pulzenus 

Prosopis  varif rons 

1,061 

131 

66 

9 
27 
13 

3 
0 
0 

0 

0 

26 

Total 

Bombus  appositus.  .  .  . 
juxtus 

94 

7 

55 

Grand  total 

1,155 

138 

121 

Third  series. — The  two  calendars  were  recorded  on  August  15  between 
8  and  11  a.  m.,  the  labor  involved  in  installation  causing  the  second  to  begin 
and  end  a  half  hour  later  than  the  first.  The  equipment  consisted  of 
8  normal  heads  of  Monarda,  3  racemes  of  Chamaenerium  and  2  of  Gilia, 
8  heads  of  Aster  bigelovi,  and  8  flowers  of  Geranium  caespitosum.  The 
flowers  of  one  head  of  Monarda  were  entirely  replaced  by  those  of  Chamae- 
nerium and  of  a  second  head  by  those  of  Gilia.  In  addition,  there  was  one 
head  of  each  type  of  mutilation,  viz,  upper  lip  removed,  upper  lip  and 
stamens  removed,  lower  lip  removed,  both  lips  cut  off,  corolla  cut  back 
to  half  its  length  in  all  but  the  marginal  row.  Finally,  a  few  paper  corollas 
of  Geranium  were  still  in  place  at  some  slight  distance.  The  normal  and 
mutilated  heads  of  Monarda  and  the  clusters  of  Chamaenerium  and  Gilia 
were  intermingled,  while  Geranium  and  Aster  were  at  one  edge. 


Calendar  1. 


8h18n 
8  22 

8  30 

8  32 

8  35 

8  36 


8  37 


8  48 
8  50 


8  51 


Clisodon,  normal  1,  1,  1. 

Bombus  appositus,  normal  5,  2,  2,  8,  1 ; 

lands  on  Gijia  merely. 
Bombus  juxtus,   normal   1;   Clisodon, 

normal  4,  2,  4. 
Argynnis,  normal  12,  16,  10,  12,  14,  11; 

Erynnis,  normal  4,  5. 
Bombus  juxtus,  normal  4,  Geranium  2; 

Clisodon,  normal  2,  1. 
Clisodon,  upper  lip  off  8;  unable  to 

land   on   flower  with   upper  lip 

and  stamens  off;  upper  lip  off  2; 

normal     3,     8;     touches     Gilia; 

Chamaenerium  1. 
Erynnis,  normal  4;  B.  juxtus,  normal 

3,    2,    4,    1 ;    Chamaenerium,    2, 

normal    1 ;    Erynnis,    normal    3, 

upper  lip  off  4,  both  lips  off  1, 

upper    lip    and    stamens    off    1; 

Argynnis  merely  lights  on  flower 

with  upper  lip  off. 
Erynnis,  normal  4,  5,  leaf,  normal  4,  8; 

Chamaenerium  1,  leaf. 
Erynnis,  normal  2,  3,  1. 
Erynnis,  upper  lip  and  stamens  off  1, 

normal  1,  3. 
Erynnis  normal  4,  1,  1,  2. 


8h53m  Clisodon,  normal  1,  3,  7,  8,  4;  inspects 
Chamaenerium  head,  4  normal 
flowers  of  head  with  middle 
flowers  shortened,  upper  lip  off  3, 
inspects  Chamaenerium. 

8  55  B.  appositus,  normal  8,  5,  8,  3,  8,  3,  9, 
1 ,  rim  flowers  of  shortened  head 
3,  Chamaenerium  1. 

8  57     Clisodon,    normal    6, 

normal  2. 

9  00     Erynnis,      normal      6 

Geranium  1. 
Erynnis,  normal  2,  1. 


1 ;    B.    juxtus, 
white     paper 


9  01 
9  04 


B.  juxtus,  normal  7,  2,  Chamaenerium 
5,  probing  1  from  the  bottom, 
normal  2,  Chamaenerium  2, 
normal  6,  1,  upper  lip  off  5, 
normal  3;  Erynnis,  normal  3, 
Gilia  1,  1,  upper  and  stamens 
off  8,  upper  off  3. 

9  07  Erynnis,  normal  8,  4,  2  normal  and  1 
shortened  corolla  of  the  same 
head,  upper  lip  and  stamens  off  9. 

9  10  B.  appositus,  normal  10,  9,  8,  7,  4,  4, 
3, 1 ;  Erynnis,  shortened  corolla  1, 
normal  12,  Chamaenerium  2; 
normal  5,  rests  on  Gilia. 


86 


NORMAL  AND  EXPERIMENTAL  POLLINATION. 


Calendar  1 

9h15m  Clisodon,  normal  2,  1,  4,  1  p.  n.,  7p, 
7p,  3n;  Chamaenerium  2,  in- 
spects 2  mutilated  heads,  normal 
4,  6  p,  12  p  twice  (total  24), 
2,  4  p,  shortened  1,  5  p,  2  p; 
B.  juxtus,  normal  3,  Chamae- 
nerium 1,  shortened  7,  inspects 
flowers  with  both  lips  off, 
normal  1,3,  1,  Chamaenerium  2, 
normal  6;  Erynnis,  upper  and 
stamens  off  4,  normal  3. 
Clisodon,  normal  2  p,  upper  lip  off  1, 
normal  3  p,  1  n,  10,  inspects 
heads  with  upper  lip  and  with 
this  and  stamens  off,  shortened 
1,  normal  3  p,  3,  4,  6,  2. 
Argynnis,  upper  off  8. 
Apis  lands  on  3  normal  heads  but  is 
unable  to  reach  nectar;  B.  juxtus, 
normal  2,  Chamaenerium  3, 
lower  lip  off  9,  working  very 
rapidly,  normal  3;  B.  appositus, 
normal  1,  3,  2,  5;  Erynnis, 
upper  lip  off  7. 
Erynnis,  normal  2. 
Argynnis,  normal  2,  upper  lip  off  6. 
Clisodon,  normal  12,  12,  13,  inspects 
Chamaenerium,  shortened  3,  15 
normal  of  shortened  head,  Cha- 
maenerium 3,  normal  1,  5,  8,  2,  4; 
B.  juxtus,  normal  10,  11,  14, 
Chamaenerium  6,  Chamaenerium 
1  (next  stalk),  shortened  6, 
Chamaenerium  head  2. 

9  35  Argynnis,  normal  3,  1,  14,  2,  4,  4; 
Erynnis,  normal  1,  touches  Gilia 
and  Chamaenerium,  lower  lip 
off  8,  leaf. 

9  39  Erynnis,  Chamaenerium  1;  normal  1, 
lower  lip  off  3,  shortened  2, 
Chamaenerium  1. 

9  40  Erynnis,  normal  5,  3,  4;  Argynnis, 
normal  5,  Chamaenerium   1. 

9  42  Argynnis,  normal  2 ;  Erynnis,  shortened 
1,  upper  lip  and  stamens  off  2, 
upper  lip  off  12,  normal  1, 
Geranium  1,  lower  lip  off  2, 
Chamaenerium  2. 


9  22 


9  25 
9  26 


9  30 
9  31 
9  33 


■Continued. 
9h45m  Argynnis,  normal  4. 
9  47     Argynnis,  upper  lip  off  12,  normal  8, 
tries    all    buds   of   young    head, 
lights  merely  on  Chamaenerium* 
9  49     B.  juxtus,  normal  1,  2,  1,  3,  Chamae- 
nerium 2;  Clisodon  normal   12, 
13;   B.    appositus,    normal   4,  5, 
shortened  4,  both  lips  off  3. 

Erynnis,  Gilia  1,  normal  3,  2;  Argynnis, 
normal  2,  5. 

B.  appositus,  normal  2,  2,  1,  1,  3,  3. 

B.  juxtus,  small  individual  tries  4 
heads  but  can  not  reach  nectar. 

Erynnis,  normal  3,  Gilia  1,  normal  3, 
lower  lip  off  4,  normal  1. 

B.  appositus,  normal  10;  Erynnis, 
normal  10,  11. 

Clisodon,  normal  4  p,  2  p,  3  p,  3  p, 
2  p,  3  n,  3  n,  2  p,  Chamaenerium 
1,  lower  lip  off  2  p,  normal  2  p, 
upper  lip  off  2  p,  1  n,  1  p,  3  p, 
2  p,  1  n. 

Erynnis,  normal  2;  Clisodon,  normal 
2  p,  1  p,  4  p,  lower  lip  off  1  p,  In, 
normal  1,  5,  1  p,  1  p,  shortened 
1  and  3  normal  of  the  same  head, 
Aster  1,  normal  4,  4. 

Erynnis,  upper  lip  and  stamens  off  1; 
B.  morrisoni,  Chamaenerium 
head  4,  shortened  1,  normal  2, 
Gilia  3;  B.  juxtus,  normal  2, 
upper  lip  and  stamens  off  3, 
upper  lip  off  4,  upper  lip  and 
stamens  off  3,  2  normal  of  short- 
ened head,  Chamaenerium  1, 
normal  4,  1,  6. 
10  06  Clisodon,  upper  lip  and  stamens  off  3, 
shortened  3,  normal  3,  4  p,  3, 
lower  lip  off  3  p,  normal  4,  1  p, 
7,  2,  shortened  1;  Argynnis, 
normal  10,  4,  5;  Erynnis,  normal 
3,  4,  3. 

Argynnis,  normal  14,  10,  shortened  3. 

Erynnis,  8  normal  of  shortened  head, 
upper  lip  off  2 ;  Argynnis,  normal 
7,  6,  shortened  2,  lower  lip  off  4. 


50 


9  52 
9  54 


9  55 
9  56 


59 


10  01 


10  03 


10  12 
10  14 


Calendar  2. 


8h40m  Bombus  hunti,  Chamaenerium  raceme 
68,  inspects  Aster,  Chamae- 
nerium raceme  16,  Atrytone 
normal  2,  2,  Chamaenerium 
raceme  2. 

Erynnis,  normal  2,  upper  lip  off  6. 

Erynnis,  upper  lip  off  2,  normal  3. 

Erynnis,  normal  10. 

Aristatus,  normal  1;  B.  morrisoni 
queen,  Chamaenerium  raceme  2; 
Erynnis  normal  6,  Gilia  1,  nor- 
mal 5. 

Erynnis,  normal  3. 

Eristalis,  Chamaenerium  raceme  1; 
Erynnis  normal  2. 


8  45 
8  46 
8  50 
8  53 


8  58 
8  59 


9h00n 
9  02 
9  08 


9  14 


9  26 


Erynnis,  upper  lip  off  7. 

Erynnis,  upper  lip  off  6. 

Erynnis,  Chamaenerium  raceme  1; 
Clisodon,  upper  lip  off  3,  normal 
4,  lower  lip  off  9,  normal  1, 
shortened  5,  upper  lip  off  10, 
normal  3,  13,  inspects  mixed 
Gilia  head,  normal  6,  4,  5. 

Erynnis,  normal  1 ;  Clisodon,  normal  1 ; 
Argynnis  inspects  1. 

Erynnis,  normal  1. 

Erynnis,  normal  4,  upper  lip  off  3; 
H.  pulzenus,  normal  2,  Aster  30 
florets  in  1  head. 

Erynnis,   Chamaenerium   raceme   3. 


MONARDA   FISTULOSA. 


87 


Calendar  2 — Continued. 


9h27m  Erynnis,  normal  6,  upper  lip  off  5, 
normal  8;  H.  pulzenus,  Aster 
16  florets  in  1  head. 

Erynnis,  upper  lip  off  10. 

Erynnis,  Aster  12  florets  in  1  head, 
Chamaenerium  raceme  20;  Ar- 
gynnis,  upper  lip  off  2. 
juxtus,  Chamaenerium  raceme  9; 
Andrena  same  Chamaenerium 
raceme  9. 

Erynnis,  normal  2;  H.  pulzenus,  Aster 
2  florets  1  head. 

Argynnis,  normal  5,  2,  upper  lip  off  4. 

B.  morrisoni,  normal  2. 

Erynnis,  normal  4,  3,  leaf;  B.  bifarius, 
Chamaenerium  raceme  25,  Gera- 
nium 1,  normal  6,  2. 
10  05     B.     morrisoni,     normal     3;   Syrphus, 
normal  4, 8,  5;  Erynnis,  normal  6. 


9  34 
9  37 


9  44     B. 


9  50 


9  53 
9  56 
9  58 


10  14 
10  17 
10  19 

10  20 
10  22 
10  24 

10  26 

10  29 
10  30 
10  34 
10  35 

10  38 

10  42 

Erynnis,  upper  lip  off  2. 

Erynnis,  normal  4. 

Argynnis,  normal  4. 

Argynnis,  upper  lip  off  2;  B.  morrisoni, 

normal  4,  7. 
Clisodon,  normal  1. 
Argynnis,  normal  5. 
H.  pulzenus  3,  Aster  florets  in  1  head; 

Erynnis,  normal  2. 
Erynnis,  normal  4,  4,  2,  2;  B.  hunti, 

Chamaenerium  raceme  6. 
Andrena,  Aster  7  florets  in  1  head. 
Erynnis,  normal  2,  3,  4. 
Erynnis,  normal  6. 
Erynnis,  normal  3;  Colletes,  Aster  2 

florets  in  1  head. 
B.    hunti,    Aster    1;    Erynnis,    normal 

8,  3,  5,  6;  Argynnis,  normal  5. 
Erynnis,  normal  1. 


Table  60. — Summary  of  calendars. 
Calendar  1. 


II 


a  ° 


l«S 


s  a 

a    <» 

a  o 


Clisodon.  .  . 

B.  appositus 
juxtus.  . . 
morrisoni 

Erynnis 

Argynnis 

Total 


151 

113 

2 

161 

187 


0 
28 
26:1 


923 


78:2i!  37 


22:lsh 
li 

3 

2 

0 
10:lsh 

0 


3:2i 

0 

o 

26 
0 


0 
0 
3 

3:2i 
0 


7:2i 

1 
25 
0 
7:1  i 

1 


37:2sh    4:li35:2: 
li 


43 


i:2i 


6:1 


41:2i 


0 

0 

0 

lw 

0 


lw 


Calendar  2. 


Clisodon 

B. juxtus.  . .  . 

morrisoni . . 

bifarius.  .  . 

hunti 

H.  pulzenus.  . 

Andrena 

Colletes 

Erynnis 

Argynnis 

A  try  tone 

Syrphus 

Aristatus 

Eristalis 

Total 

Grand  total. 


38 

13 

0 

0 

16 

0 

8 

0 

0 

0 

2 

0 

0 

0 

0 

0 

125 

41 

21:1  i 

8 

4 

0 

17 

0 

1 

0 

0 

0 

232:1 i      62 


1,155: 1  il   140:2 i;  46       37:2sh    4:li'35:2i    48 


6:li203:2; 


1 

0 

0 

0 

0 

0 

1 

0 

0 

1:1 

0 

51 

0 

7 

0 

2 

0 

12 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

1      73:li 


4      74:1 i 


88 


NORMAL  AND  EXPERIMENTAL  POLLINATION. 
Table  61. — General  summary. 


Species 

Normal 

Total 
muti- 
lated. 

Total 

other 

flowers. 

Species 

Normal 

Total 
muti- 
lated. 

Total 

other 

flowers. 

309 
151 
113 
2 
161 
187 

51 

7 
37 

1 
77 
35 

8 

1 
29 

7 
11 

1 

Bombus  hunti 

Halictus  pulzenus. . 

0 
2 
0 
0 
125 

21 
4 

17 
1 
0 

0 
0 
0 
0 
41 
8 
0 
0 
0 
0 

91 
51 
16 
2 
37 
0 
2 
0 
0 
1 

Bombus  appositus.  . 

juxtus 

morrisoni.  . 

Colletes 

Total 

923 

208 

57 

38 
0 
16 

8 

27 
0 
0 
0 

0 

9 

2 

26 

Bombus  juxtus 

morrisoni .  . 
bifarius. . .  . 

Total 

Grand  total . 

232 

76 

237 

1,155 

284 

294 

Table  62. — Summary  of  tables;  mutilations  and  totals. 


Species. 

Norm. 
Mon. 

Upper 
lip 
off. 

Upper 

and  sta. 

off. 

Lower 
lip 
off. 

Both 
lips 
off. 

Corolla 
short. 

Total 
mutila- 
tions 

Total 

compet- 
itors. 

1,009 

405 

8 

1 

40 

220 

0 

31 

0 

0 

0 

6 

2 

0 

388 

224 

37 

7 

1 

0 

18 

56 
17 
0 
0 
3 
10 
0 
0 
0 
0 

0 
0 
0 
0 
97 
35 
2 
0 
0 
0 
0 

18 
1 
0 
0 
0 
9 
0 
0 
0 
0 

0 
0 
0 
0 
18 
4 
8 
0 
0 
0 
0 

9 
7 
0 
0 
0 
46 
0 
0 
0 
0 

0 
0 
0 
0 
39 
0 
0 
0 
0 
0 
0 

0 
7 
0 
0 
0 

1 

0 
0 
0 
0 

0 
0 
0 
0 
3 
0 
0 
0 
0 
0 
0 

25 
4 
1 
0 
0 

16 
0 
1 
0 
0 

0 
0 
0 
0 
4 
6 
3 
0 
0 
0 
0 

110 
36 
1 
0 
3 
82 
0 
1 
0 
0 

0 

0 

0 

0 

162 

45 

13 

0 

0 

0 

0 

9 

9 
35 

0 
101 
65 
25 
10 
16 

2 

2 

52 

0 

6 

98 

10 

8 

0 

0 

1 

0 

Bombus  appositus.  .  . 

bifarius 

edwardsi . . . 

hunti 

juxtus 

occidentalis . 
morrisoni . .  . 

Colletes 

Halictus  (Lasioglos- 
sum)  sp.. 
pulzenus.  .  . 
Monumetha 

Eristalis 

Grand  total.  . 

2,397 

220 

58 

101 

11 

60 

453 

449 

SUMMARY. 

Although  the  flowers  of  Monarda  are  in  heads,  they  are  sufficiently 
separated  that  bees  and  the  smaller  butterflies  must  fly  from  one  to  another, 
and  are  thus  fairly  comparable  with  those  of  other  species.  However,  the 
detailed  consideration  of  the  relation  to  competing  flowers  is  deferred  to 
the  succeeding  chapter,  the  totals  only  being  taken  into  account  here  for 
the  sake  of  a  view  of  the  entire  experiment.     The  number  of  visits  to  muti- 


RESUME.  89 

lated  flowers  of  Monarda  and  to  flowers  of  other  species  was  practically  the 
same,  though  this  is  doubtless  only  a  coincidence.  The  normal  flowers 
were  about  thrice  as  attractive  as  these  two  groups,  due  in  part  to  habit 
and  in  part  to  the  mutilated  ones  being  often  less  conspicuous  and  demanding 
unusual  methods  of  approach. 

The  number  of  visits  to  the  various  mutilations  were  determined  by 
four  factors,  namely,  conspicuousness,  ease  of  landing,  accessibility,  and 
exposure  of  nectar.  Flowers  with  the  upper  lip  removed  were  visited, 
most,  since  they  were  least  changed  in  essential  respects,  the  lower  lip 
constituting  the  landing-platform  and  the  attractive  banner.  The  removal 
of  the  stamens  in  addition  diminished  the  visits  more  than  half,  by  affecting 
landing  and  eliminating  the  attraction  of  pollen,  in  the  case  of  Clisodon 
especially.  Visits  to  flowers  without  the  lower  lip  were  about  a  fourth  as 
numerous  as  to  those  with  the  upper  lip  removed,  due  to  their  being  less 
conspicuous  and  deprived  of  the  landing-platform.  Blossoms  with  the  corolla 
shortened  to  half  its  normal  length  received  an  equal  number  of  visits,  a 
puzzling  fact  when  taken  in  conjunction  with  the  response  to  flowers  with 
both  lips  cut  off.  The  difference  here  is  evidently  to  be  explained  by  the 
greater  readiness  with  which  the  odor  of  the  nectar  escapes,  as  well  as  by  the 
greater  ease  of  access  for  certain  bees.  The  respective  values  of  the  upper 
lip,  stamens,  lower  lip,  and  both  lips  in  attraction  and  guidance  are  probably 
well  indicated  by  the  number  of  visits,  viz,  220,  101,  58,  and  11. 

While  Monarda  exhibits  a  wide  range  of  visitors,  only  8  of  these  are 
frequent  and  5  important,  namely,  Clisodon,  Bombus  appositus,  B.  juxtus, 
Erynnis,  and  Argynnis.  Clisodon  paid  nearly  as  many  visits  to  the  normal 
flowers  as  the  total  for  the  other  four  species,  but  it  made  only  1  visit  in  10 
to  the  mutilated  flowers  in  contrast  to  about  1  to  2  for  Erynnis  and  1  to  3 
for  B.  juxtus.  Its  large  number  of  visits  is  to  be  explained  chiefly  by  the 
fact  that  many  of  them  were  made  for  pollen  alone  and  did  not  involve 
landing.  It  is  interesting  to  note  that  the  longer-tongued  B.  appositus 
visited  nearly  twice  as  many  normal  flowers  as  juxtus,  while  it  went  to  only 
1  mutilated  flower  in  9  to  1  in  3  for  juxtus.  Among  the  butterflies,  Erynnis 
visited  more  than  a  half  again  as  many  normal  flowers  as  Argynnis,  but  four 
times  as  many  mutilated  ones.  In  spite  of  its  apparently  less  accurate 
movements,  Erynnis  was  considerably  more  successful  than  B.  juxtus  and 
several  times  more  so  than  Argynnis  in  solving  the  difficulties  presented  by 
the  mutilated  flowers. 

RESUME. 

Variation  in  number  of  visits. — The  special  studies  of  the  abundance 
of  visitors  and  the  frequence  of  visits  made  with  Rubus  deliciosus,  Geranium 
caespitosum,  Chamaenerium  angustifolium,  and  Pentstemon  glaber  show  that 
time,  place,  and  conditions  produce  great  fluctuations  in  the  species  and 
numbers  of  visitors  and  visits.  Considerable  differences  in  these  respects 
between  early,  mid,  and  late  season  would  be  expected,  but  almost  as  great 
differences  may  be  found  between  successive  days  or  hours,  as,  for  example, 
in  the  case  of  Chamaenerium,  where  the  number  of  visitors  and  visits  for 
two  successive  hours  were  21:728  and  4:204,  or  of  Rubus  deliciosus,  for 
which  the  figures  for  Apis  were  22:127  and  5:5.     The  effect  of  even  a 


90  NORMAL  AND  EXPERIMENTAL  POLLINATION. 

small  distance  is  shown  in  the  Monarda  calendars,  which  were  made  in 
areas  but  3  meters  apart.  The  flower  group  was  essentially  similar  in  both, 
but  one  calendar  gave  1,061  visits  to  normal  Monarda,  131  to  the  mutilated, 
and  66  to  other  species,  while  the  other  made  simultaneously  yielded  94 
normal  visits,  7  mutilated,  and  55  to  competing  flowers.  Essentially 
similar  results  were  obtained  the  next  day,  the  first  area  giving  923,  208, 
and  57  visits  respectively,  and  the  second  232,  76,  and  237.  It  is  thus 
evident  that  a  single  record  or  calendar  can  not  give  an  accurate  or  com- 
prehensive picture  of  the  numerical  relations  between  a  group  of  flowers 
and  insects.  It  is  evident  also  that  similar  variations  must  be  more  or 
less  universal,  and  that  they  often  explain  the  discrepancies  between  the 
results  of  different  investigators. 

Changes  of  position. — In  general,  the  problem  of  alighting  and  securing 
nectar  from  flowers  in  inverted,  horizontal,  vertical,  or  other  changed 
positions  was  solved  with  more  or  less  readiness  by  the  various  bees.  The 
general  behavior  is  well  illustrated  by  the  response  to  such  changes  in 
Aconitum.  Bombus  juxtus  and  B.  bifarius  readily  entered  flowers  with  the 
hood  pointed  downward,  though  this  involved  using  the  side  petals  instead 
of  the  lower  sepals  as  a  landing  platform.  When  the  hood  was  turned  to 
the  side,  B.  juxtus  first  hovered  over  such  flowers  for  a  moment  before  landing 
successfully;  in  one  case  it  slipped  off,  but  tried  again  and  succeeded.  In 
the  case  of  inverted  flowers,  some  individuals  passed  over  them,  others 
hovered,  and  still  others  attempted  to  light  and  then  flew  away  as 
though  disturbed  by  the  change.  Some  landed  at  the  lower  sepals,  turned 
around,  and  entered  upside  down;  at  other  inverted  flowers  they  behaved 
in  exactly  the  same  way,  apparently  recognizing  the  changed  position  before 
landing.  One  individual  landed  three  times  at  a  group  of  inverted  blossoms, 
tried  to  reach  the  nectary  without  turning  upside  down,  and  failed  in  every 
case.  One  B.  bifarius  mastered  the  problem  readily  and  went  to  five 
inverted  flowers  in  succession,  turning  upside  down  just  after  alighting. 

A  scrutiny  of  the  behavior  of  various  species  of  bees  when  confronted 
by  changes  in  the  position  of  flowers  makes  it  certain  that  they  usually 
recognize  such  changes  at  once.  Since  these  are  essentially  changes  in 
form,  they  demonstrate  that  such  insects  at  least  do  distinguish  forms. 
Differences  in  specific  behavior  are  shown  by  table  50,  in  which  Apis  paid 
relatively  almost  twice  as  many  visits  to  inverted  as  to  normal  flowers, 
Pseudomasaris  about  half  as  many,  and  Bombus  went  about  equally  to  the 
two.  Differences  in  individual  behavior  are  exemplified  by  the  instances 
given  above  for  Bombus  and  they  are  revealed  as  well  by  practically  all 
studies  with  changes  of  position.  They  permit  no  doubt  of  the  remarkable 
intelligence  of  bees  in  problems  that  arise  in  situations  with  which  they  are 
familiar.  It  seems  obvious  also  that  many  of  the  individual  variations  in 
response  are  not  the  result  of  differences  in  intelligence,  but  rather  in  what 
is  called  temperament  in  man. 

Masking  with  cotton. — When  the  center  of  the  flower  was  masked  with 
cotton,  or  cotton  plugs  put  over  or  in  the  nectaiies,  the  bees  were  usually 
unsuccessful  in  reaching  the  nectar  or  pollen.  Most  of  them  landed  and 
probed  where  the  nectary  or  stamens  should  be,  but  were  unable  to  reach 


RESUME.  91 

these  except  where  they  found  an  entrance  at  the  edge.  After  making  vain 
attempts  at  one  or  two  masked  flowers,  they  usually  hovered  over  others, 
apparently  inspecting  them  in  the  light  of  their  previous  experience.  The 
presence  of  a  strange  substance  in  the  flower  changed  the  relations  so  greatly 
and  offered  an  obstancle  so  foreign  to  the  experience  of  the  bee  that  it  could 
be  solved  in  but  few  cases.  Their  behavior  demonstrated  the  good  memory 
of  bees  for  position  in  the  flower,  and  their  ignoring  of  the  masked  flowers, 
both  with  and  without  experience  of  the  cotton  as  an  obstacle,  indicated 
their  perception  of  form. 

Mutilation. — In  more  than  three- fourths  of  the  experiments  mutilated 
flowers  were  visited  to  a  greater  extent  than  the  normal  ones,  the  outstanding 
exception  being  Monarda,  to  which  the  normal  visits  were  five  times  more 
numerous  than  those  to  the  mutilated  flowers.  The  advantage  enjoyed 
by  the  mutilated  flowers  as  a  whole  was  due  chiefly  to  those  in  which  both 
stamens  and  styles  were  excised  or  all  parts  removed  but  the  ovary  and 
nectaries.  These  changes  not  only  permitted  the  odor  of  the  nectar  to 
escape  more  freely,  but  also  made  the  nectar  itself  more  readily  accessible, 
with  the  consequence  that  the  bees  could  work  more  flowers  in  the  same  time, 
and  were  also  led  to  return  to  them  sooner.  Increasing  the  attractive  surface 
of  the  perianth  also  augmented  the  number  of  visits;  for  example,  splitting 
the  hood  of  Aconitum  and  turning  the  sepals  back  rendered  such  flowers 
more  than  four  times  as  attractive  as  the  normal  ones.  On  the  contrary, 
reducing  the  expanse  of  the  corolla  to  a  half  diminished  its  attraction  from 
one-half  to  a  tenth  in  practically  all  cases  and  demonstrated  its  paramount 
importance  even  in  the  case  of  habituated  bees.  When  both  lips  were 
removed  in  Monarda,  the  number  of  visits  was  reduced  to  a  fortieth  of  the 
total  for  all  mutilations,  though  the  difficulty  of  landing  obviously  played 
some  part  in  the  result.  The  removal  of  the  lower  lip  alone  decreased  the 
visits  to  a  fourth  of  those  to  flowers  with  the  upper  lip  alone  removed  and  to 
a  tenth  of  the  total  visits  to  mutilations. 

The  accounts  of  the  behavior  of  the  different  species  and  of  the  individuals 
of  each  species  to  the  various  mutilations  naturally  reveal  similar  specific 
and  individual  differences  to  those  found  for  changes  of  position,  and  these 
are  shown  most  clearly  for  Monarda  in  table  62.  Clisodon  paid  only  1  visit 
in  10  to  the  mutilated  flowers  in  contrast  to  about  1  to  2  for  Erynnis  and 
1  to  3  for  Bombus  juxtus.  In  contrast  to  the  last,  B.  morrisoni  made  1  visit 
in  30  to  mutilated  ones,  while  B.  occidentalis  went  to  neither  normal  nor 
mutilated  Monarda,  but  only  to  flowers  of  competing  species.  There  was 
no  striking  difference  between  the  general  behavior  of  Bombus  on  the  one 
hand  and  the  butterflies  on  the  other.  With  respect  to  the  type  of  mutila- 
tion most  visited,  Erynnis,  B.  appositus,  and  B.  juxtus  went  to  each  of  the 
5  types,  Clisodon  to  4,  and  Argynnis  to  but  3.  Of  the  mutilated  flowers 
Clisodon  gave  the  preference  to  those  with  the  upper  lip  removed,  as  did 
B.  appositus;  B.  juxtus  preferred  those  with  the  upper  lip  and  stamens  cut 
away,  while  both  Erynnis  and  Argynnis  likewise  went  most  often  to  the 
flowers  without  an  upper  lip,  the  removal  of  the  latter  obviously  interfering 
least  with  attraction  and  access. 

The  evidence  of  this  table,  as  well  as  that  from  the  mutilation  experi- 
ments as  a  whole,  leaves  no  doubt  that  these  pollinators  were  able  to  dis- 


92  NORMAL  AND  EXPERIMENTAL  POLLINATION. 

tinguish  the  form  of  the  different  types  and  to  adjust  themselves  to  the 
changes  with  a  great  deal  of  ingenuity.  What  is  now  most  needed  is  quanti- 
tative studies  of  marked  individuals,  both  old  and  young,  to  determine 
differences  in  normal  response  and  learning  power. 

Artificial  flowers. — The  artificial  flowers  employed  were  always  com- 
posite in  nature,  consisting  of  crepe-paper  corolla  or  perianth  surrounding 
the  natural  center  of  the  flower  concerned,  or  more  rarely  of  a  natural 
flower  or  head  with  a  paper  disk  below  it.  These  imitations  were  at  once 
rather  more  crude  than  those  used  by  Plateau,  Andreae,Wery.  and  others, 
in  so  far  as  the  attractive  corolla  was  concerned  and  much  more  natural 
with  respect  to  stamens  and  pistil.  As  a  rule,  they  were  visited  little  or 
not  at  all,  receiving  but  257  visits  in  comparison  with  more  than  2,000  to 
normal  flowers,  and  a  fifth  of  these  were  paid  Frasera  flowers  provided 
with  Campanula  petals.  In  more  than  a  half  of  the  installations  the 
imitations  were  completely  ignored  or  received  but  2  or  3  visits.  The 
best  success  was  obtained  with  Rosa,  in  which  the  relation  between  visits 
to  natural  and  artificial  flowers  was  257 :  78,  Rubus  deliciosus,  where  it  was 
254:49,  and  Geranium,  where  it  was  63:37,  though  the  imitations  were 
5  times  more  numerous.  In  the  case  of  the  Frasera-Campanula  composite, 
this  received  56  visits  to  97  for  the  normal,  proving  that  the  use  of  natural 
tissues  was  much  less  disturbing  than  that  of  paper.  However,  it  is  certain 
that  the  paper  corollas  did  not  in  themselves  actually  repel  the  bees,  since 
Bombus  in  particular  went  readily  to  paper  Mentzelias  in  the  early  evening 
before  the  natural  ones  were  open. 

There  was  the  usual  wide  range  in  the  behavior  of  the  various  genera. 
Halictus  pulzenus  went  indifferently  to  paper  and  natural  roses,  Bombus 
juxtus  visited  practically  as  many  Frasera  flowers  with  Campanula  petals 
as  normal  ones,  and  B.  bifarius  went  to  more  than  half  as  many  artificial 
as  natural  Geranium  flowers.  Osmia  was  likewise  a  frequent  visitor  to  the 
imitations.  On  the  other  hand,  no  honey-bees  were  seen  to  visit  artificial 
flowers,  though  they  often  were  deceived  until  they  came  near,  as  shown  by 
the  fact  that  such  flowers  were  much  inspected.  Prosopis  and  Andrena 
made  very  few  visits  to  the  paper  flowers.  Very  few  flies  and  butterflies 
were  present  in  these  experiments  and  the  visits  were  too  infrequent  to 
indicate  their  response. 

The  significant  fact  is  that  crude  paper  composites  were  visited  freely 
by  a  few  species  and  that  some  flowers  were  frequently  visited  as  imitations 
and  others  not  at  all.  While  the  results  as  a  whole  approach  more  nearly 
those  of  Plateau  and  Forel  than  those  of  Andreae,  Wery,  Giltay,  Detto, 
and  others,  it  is  clear  that  they  constitute  the  explanation  of  the  discrepancy 
between  them,  as  is  shown  more  fully  in  the  final  resume1  in  Chapter  4. 
The  artificial  flowers  were  sufficiently  plausible  to  cause  a  large  number 
of  inspections,  which  signifies  that  the  marks  differentiating  them  could  not 
be  distinguished  until  the  insect  was  within  a  few  centimeters.  The  case 
of  Mentzelia  shows  that  they  did  not  repel  visitors  and  that  the  difference 
is  rather  one  of  habit. 

Painted  flowers. — These  were  much  more  successful  than  artificial 
flowers  in  attracting  visitors  in  competition  with  natural  ones,  receiving 


RESUME.  93 

420  visits  to  845  for  the  latter.  In  the  case  of  Aconitum  they  obtained 
154  visits  to  116  for  the  normal  flowers,  though  they  were  more  numerous 
in  the  installation.  This  was  likewise  true  of  Chamaenerium,  the  numbers 
being  111  to  103,  though  on  the  basis  of  the  number  of  each  the  relation 
is  44 :  103.  The  painted  flowers  of  Rubus  deliciosus  were  visited  as  frequently 
as  the  natural  ones,  while  in  the  case  of  Frasera  the  visits  were  a  half  and  in 
that  in  Delphinium  a  fifth  as  many  as  for  the  natural. 

The  outstanding  visitor  to  the  painted  flowers  was  Bombus  juxtus,  which 
made  more  than  half  the  total  number  of  visits.  However,  in  two  experi- 
ments it  was  exceeded  by  the  honey-bee,  which  made  27  such  visits  to  its  12. 
The  27  visits  were  in  contrast  to  67  for  the  normal  flowers,  thus  showing 
clearly  how  much  more  natural  the  painted  flowers  appeared  than  the  paper 
ones,  since  Apis  did  not  visit  a  single  one  of  the  latter.  Of  the  four  colors 
most  employed,  blue  obtained  a  distinct  preference,  the  visits  being,  blue  98, 
green  84,  yellow  55,  and  red  43. 

The  painted  flowers  were  approximately  five  times  as  successful  in 
attracting  bees  as  the  paper  ones.  This  was  due  to  their  identity  with  the 
natural  ones  in  everything  but  color,  and  indicates  that  the  artificial  flowers 
were  distinguished  as  such  chiefly  by  small  differences  in  form  and  by  the 
texture,  thus  demonstrating  an  acute  perception  of  form  and  texture  by 
Bombus  and  A  pis  especially.  The  significance  of  this  is  further  discussed 
in  the  final  r6sume\ 

Honey  and  odor. — In  the  majority  of  the  species  where  it  was  employed, 
honey  actually  decreased  the  number  of  visits,  often  tenfold,  while  in  a  few 
it  had  no  discernible  effect.  In  no  case  did  it  increase  the  number  of  visits 
to  natural  flowers,  and  it  had  practically  no  effect  upon  those  to  artificial 
ones.  The  significant  result  of  these  experiments  was  to  confirm  the  evi- 
dence of  the  exceedingly  poor  sense  of  smell  in  bees  for  honey.  Often  they 
would  not  discover  the  drop  at  a  distance  of  a  few  millimeters  and  in  some 
cases  they  even  became  entangled  in  it  without  recognizing  it.  This  may 
have  been  due  to  the  odor  of  the  flower  itself,  but  as  it  was  true  of  all 
the  flowers  employed,  it  suggests  that  the  odor  of  nectar  plays  a  very  small 
part  in  the  attraction  exerted  by  many  species. 

The  addition  of  perfumes  derived  from  other  flowers  or  of  other  odorous 
substances  decreased  the  total  of  visits  50  per  cent  in  comparison  with 
normal  flowers.  Even  when  honey  was  also  added,  a  similar  relation 
obtained,  though  it  is  certain  if  the  bees  had  been  trained  to  come  for 
honey  on  flowers  with  a  certain  perfume  that  the  latter  would  have  seemed 
attractive.  With  odor,  as  with  color,  form,  and  texture,  habit  is  the  con- 
trolling factor,  and  this  probably  explains  why  the  various  perfumes  ap- 
peared to  repel.  They  disturbed  the  habitual  response  of  the  bee,  and 
this  was  true  whether  perfumes,  essences,  or  odors  unpleasant  to  us  were 
employed.  The  results  certainly  do  not  strengthen  the  role  of  odor  in 
attraction,  though  undoubtedly  it  often  plays  a  part  in  forming  the  habit 
of  guidance. 


3.  COMPETITION  AND   CONSTANCY. 

Significance. — Although  a  number  of  studies  have  been  made  with 
special  reference  to  the  constancy  of  a  particular  species  of  pollinator  to 
one  species  of  flower,  there  has  been  little  or  no  experimental  work  in  this 
field.  Competition  between  different  species  or  genera  of  plants  for  the 
visits  of  insects  has  received  practically  no  attention  and  no  experiments 
are  known  that  bear  directly  upon  this  problem.1  The  early  view  that  the 
bees  in  particular  are  constant  or  nearly  so  has  been  shown  to  be  only  partly 
true  by  Bulman,  Plateau,  and  others,  and  the  whole  subject  of  habit  in 
pollinators  has  been  found  to  be  much  more  complex  than  supposed.  The 
idea  that  constancy  was  essential  to  the  effective  cross-pollination  of  a 
species,  as  well  as  to  the  prevention  of  hybridization,  has  necessarily  been 
modified,  and  is  now  rather  to  be  regarded  as  a  matter  for  investigation 
in  terms  of  habit  and  efficiency.  Moreover,  there  have  been  several  dif- 
ferent concepts  of  constancy,  as  discussed  later.  In  the  present  treatment, 
the  experimental  results  of  competition  studies  are  first  considered.  This 
is  followed  by  an  account  of  the  composition  and  weight  of  the  pollen  loads 
of  various  species,  and  the  chapter  is  concluded  with  a  resume  of  the  work 
of  other  investigators  and  a  summary  of  the  general  principles  involved. 

COMPETITION. 

General  plan. — The  methods  employed  in  competition  experiments 
have  been  discussed  in  detail  in  the  introduction,  the  one  most  used  in  the 
present  study  being  that  of  reciprocal  bouquets.  The  primary  objectives 
have  been  to  throw  light  on  the  degree  of  habit  fixation  on  the  one  hand 
and  to  furnish  evidence  as  to  the  relative  attractiveness  of  different  flowers 
on  the  other.  At  the  same  time,  questions  of  efficiency  have  been  taken  into 
account.  For  the  most  part,  the  species  with  regular  corollas  were  used  in 
order  that  visitors  might  not  be  excluded  or  handicapped  by  structural 
features,  but  a  few  zygomorphic  flowers  were  employed  in  order  to  disclose 
the  effect  of  structure. 

The  bouquet  method  was  the  one  regularly  used,  though  occasionally 
normal  plants  grew  sufficiently  close  to  each  other  that  equal  areas  or  equal 
numbers  of  flowers  could  be  marked  off  for  comparison.  In  all  cases  the 
natural  plant  was  regarded  as  the  standard,  and  the  comparison  was  made 
by  means  of  a  bouquet  placed  in  its  midst  or  attached  to  the  branches. 
The  bouquet  consisted  in  some  cases  of  a  mass  of  flowers  or  a  group  of 
branches  and  in  others  of  single  flowers  or  branches  put  in  vials  and  attached 
to  the  stems.  In  practically  all  cases  where  this  method  was  used,  the 
records  were  made  in  the  normal  habitat  of  the  standard  plant.  The 
bouquets  were  arranged  among  the  stems  or  branches  so  that  the  insects 
would  necessarily  pass  them  in  moving  about.  In  a  few  instances  the 
bouquet  consisted  of  several  species  from  other  localities,  in  order  to  deter- 
mine the  reaction  to  species  probably  not  seen  previously  but  similar  to 
those  regularly  visited. 

1  Knoll  has  made  an  incidental  study  of  competition,  which  has  just  come  to  hand  (1922: 
215);  he  employed  Pelargonium  zonale  or  Satureia  nepeta  in  competition  with  Linaria  vulgaris 
in  experiments  with  Macroglossa  stellatarum. 

94 


RUBUS   STRIGOSUS.  95 


RUBUS  STRIGOSUS. 


General  relations. — The  raspberry  is  especially  well  fitted  to  serve  as 
a  standard  plant  for  competition  studies,  owing  to  its  abundant  nectar  and 
pollen,  the  duration  of  the  flowering  period,  and  its  exceptional  attractiveness 
for  the  honey-bee.  While  it  is  employed  as  the  standard  plant  for  the 
majority  of  the  following  experiments,  certain  reciprocal  comparisons  were 
made  in  which  it  was  the  bouquet.  The  various  species  with  which  it 
competed  practically  all  possess  open  flowers,  but  exhibit  a  wide  range  in 
the  size  and  color  of  the  latter  and  the  amount  of  nectar  and  pollen,  as  well 
as  in  the  degree  of  relationship.  With  respect  to  the  latter,  Rubus  deliciosus 
represents  a  related  species,  Rosa  a  related  and  Opulaster  a  more  distant 
genus  of  the  same  family,  while  Geranium,  Cleome,  and  Frasera  are  succes- 
sively more  remote,  exemplifying  a  progressive  decrease  in  the  number  of 
stamens  and  pistils,  as  well  as  striking  differences  in  the  nectaries.  Mer- 
tensia  and  Pentstemon  afford  more  pronounced  differences,  though  these  are 
still  within  the  range  of  effective  competition.  The  order  of  treatment  in 
the  following  pages  is  essentially  that  of  degree  of  relationship,  though  the 
effect  of  size,  color,  and  amount  of  nectar  or  pollen  often  obscures  the  signi- 
ficance of  this. 

RUBUS  STRIGOSUS  AND  RUBUS  DELICIOSUS. 

Comparison. — The  flowers  of  the  raspberry  are  small  and  inconspicuous 
and  more  or  less  hidden  by  the  leaves,  so  that  they  are  hardly  noticeable, 
while  those  of  the  salmonberry  are  large  and  showy  and  stand  out  clearly 
from  the  leaves  on  most  of  the  branches.  The  flowers  of  both  are  white, 
but  the  corolla  of  Rubus  strigosus  is  masked  to  a  large  degree  by  the  green 
sepals.  The  flowers  of  the  latter  are  often  more  numerous  in  an  equal 
area,  but  they  are  so  scattered  as  to  be  quite  ineffective.  Pollen  is  naturally 
abundant  in  both  species,  but  there  is  approximately  eight  times  as  much 
in  R.  deliciosus.  The  petals  of  the  latter  are  expanded  at  right  angles  to 
the  pedicel,  leaving  the  stamens  much  exposed,  while  in  R.  strigosus  the 
petals  are  more  or  less  erect  and  the  pollen  consequently  less  accessible. 
The  nectar  of  R.  deliciosus  is  formed  at  the  base  of  the  stamens  and  appears 
as  minute  drops  in  a  circle;  it  is  produced  in  the  same  place  in  R.  strigosus, 
but  much  more  abundantly,  sometimes  accumulating  to  an  appreciable 
depth  in  the  stamen-tube  (plate  3). 

Experiments. — Of  the  five  studies  made  with  these  two  species,  Rubus 
strigosus  was  employed  as  the  standard  plant  in  the  first  three,  and  R. 
deliciosus  in  the  last  two.  Two  observers  recorded  the  visitors  in  each 
case,  and  the  numbers  consequently  are  not  only  exact,  but  they  are  also 
maximum.  In  all  cases  where  two  figures  are  separated  by  a  colon,  the 
first  indicates  the  number  of  insects  and  the  second  the  number  of  visits 
made  by  them. 

The  differences  arising  out  of  the  time-factor  are  revealed  by  the  totals, 
the  number  of  visitors  being  nearly  twice  as  great  in  the  first  experiment. 
During  the  third  period,  Rubus  deliciosus  received  several  times  as  many 
visitors,  due  in  part  to  the  presence  of  the  two  species  of  flies.  All  told, 
Apis  furnished  171  visitors  to  the  raspberry  in  contrast  to  5  for  the  salmon- 


96 


COMPETITION  AND  CONSTANCY. 


berry,  while  Bombus  yielded  7  and  6  respectively.  The  total  number  of 
visiting  bees  was  212  for  the  one  and  21  for  the  other,  while  the  flies  went 
to  R.  deliciosus  alone  to  the  number  of  6. 

Table  63. — Competition  of  Rubus  strigosus  and  R.  deliciosus. 
Experiment  1,  one  hour,  10  to  11  a.m.,  July  6. 
Experiment  2,  one  hour,  ^SO"  to  10h30m  a.m.,  July  7. 
Experiment  3,  one  hour,  lO^O"1  to  llh10m  a.m.,  July  6. 


Species. 

Plant,  R. 
strigosus. 

Bouquet,  R. 
deliciosus. 

Species. 

Plant,  R. 

strigosus. 

Bouquet,  R. 
deliciosus. 

First  experiment: 

73 
5 
4 
2 
2 
2 

1 
7 
0 

7 

0 
0 
1 
1 
0 
0 

0 
0 

1 

0 

Second  experiment — Cont.: 

Ancistrocerus  sp 

Calliphora  vomitoria .  .  . 
Syrphus  americanus.  .  .  . 

Total 

1 
0 
0 

0 
4 
2 

Andrena  crataegi 

vicina 

proximus 

Colletes  oromontis 

Halictus  (Lasioglossum) 

62 

48 
1 
2 
1 
2 
2 

18 

2 
2 
2 
0 
0 
0 

One    juxtus    visited    a 
flower    of    deliciosus 
thrice    in   succession 
and  later  returned. 
Third  experiment: 

Prosopis  basalis 

varifrons 

Total 

103 

50 
2 
2 
3 
4 

3 

3 
3 

4 
2 
0 

Halictus  pulzenus 

Second  experiment: 

Pseudomasaris  vespoides 
Ancistrocerus  sp 

Total 

Halictus  pulzenus 

56 

6 

Pseudomasaris  vespoides 

Table  64. — Competition  of  R.  deliciosus  and  strigosus. 


First  experiment,  one  hour,  9  to  10  a.m., 
June  27. 

Second  experiment,  one  hour,  9  to  10  a.m., 
June  28. 

Species. 

Plant, 
R.  deli- 
ciosus. 

Bouquet, 
R.  stri- 
gosus. 

Species. 

Plant 
R.  deli- 
ciosus. 

Bouquet, 
R.  stri- 
gosus. 

Apis  mellifica 

Andrena  crataegi .... 

vicina 

Bombus  bifarius 

juxtus 

proximus. .  .  . 
Halictus  evylaeus. . .  . 
Monumetha  albifrons. 

Osmia  bruneri 

melanotricha . . 
Melitaea  sp 

Total 

4 
4 
1 
10 
0 
1 
2 
0 
6 
1 
1 

50 
0 
3 
7 
1 
6 

Apis  mellifica 

Bombus  juxtus 

morrisoni.  .  . 
Syrphus  americanus. . 

12:53 
6:26 
2:77 
1:1 

6:39 
3:26 

0 

0 

Total 

21:157 

9:65 

0 
1 
10 
0 
0 

30 

78 

In  spite  of  the  fact  that  it  was  the  bouquet  and  hence  out  of  place,  the 
total  number  of  visitors  to  R.  strigosus  was  87  in  comparison  with  51  for 
R.  deliciosus.     These  were  all  bees,  the  single  fly  and  butterfly  going  to 


RUBUS   STRIGOSUS.  97 

R.  deliciosus,  as  would  be  expected.  Of  Apis,  56  individuals  went  to  the 
raspberry  and  16  to  the  salmonberry,  the  preponderance  of  the  former 
being  reversed  in  the  second  experiment.  The  number  of  visitors  belonging 
to  Bombus  was  nearly  the  same  for  both  experiments,  viz,  17  and  19,  and 
they  were  also  more  abundant  on  R.  strigosus  in  the  first  case  and  on  R. 
deliciosus  in  the  second.  The  ratio  of  attraction  to  bees  was  almost  exactly 
the  reverse  in  the  two  instances.  It  is  also  interesting  to  note  that  they  made 
an  average  of  7  visits  to  the  raspberry  to  4  for  the  salmonberry. 

Summary. — Rubus  strigosus  is  evidently  much  more  attractive  than 
R.  deliciosus,  as  shown  bj'  the  fact  that  the  total  number  of  visitors  in  the 
five  periods  was  four  times  greater.  However,  this  was  true  only  for  the 
bees,  though  they  furnished  nearly  the  entire  number,  since  the  flies  and 
butterflies  went  only  to  the  more  visible  and  accessible  flowers  of  the  salmon- 
berry. The  raspberry  held  its  advantage,  whether  used  as  the  standard 
plant  or  the  bouquet,  except  in  the  last  experiment,  where  twice  as  many 
bees  went  to  R.  deliciosus.  The  constancy  of  the  honey-bee  was  high  in 
the  first  four  cases,  viz,  221  visitors  for  R.  strigosus  to  9  for  R.  deliciosus, 
but  it  was  in  abeyance  in  the  last,  in  which  twice  as  many  went  to  the  latter 
as  to  the  former.  As  a  whole,  Bombus  was  inconstant,  24  going  to  the  one 
and  23  to  the  other,  while  the  numbers  for  the  other  bees  were  too  small 
to  be  significant,  twice  as  many  preferring  R.  strigosus,  however. 

RUBUS  STRIGOSUS  AND  OPULASTER. 
Comparison. — The  flowers  of  Opulaster  are  about  half  as  large  as  those 
of  the  raspberry,  but  this  is  more  than  offset  by  their  grouping  in  corymbs 
and  the  position  of  the  latter  at  or  near  the  ends  of  the  branches.  The 
spreading  petals  make  the  corymb  verjr  conspicuous,  and  at  a  distance  it 
assumes  a  uniformly  white  appearance.  The  nectar  is  less  abundant  in 
Opulaster,  but  this  is  somewhat  compensated  by  the  large  number  of  flowers 
in  a  cluster  and  by  the  open  nature  of  the  cup.  The  stamens  are  also 
less  numerous  and  the  amount  of  pollen  available  is  considerably  less. 

Summary. — The  total  number  of  visitors  was  138  for  Rubus  and  137 
for  Opulaster,  indicating  that  they  are  equally  attractive.  However,  the 
former  was  more  than  twice  as  attractive  to  bees,  the  ratio  being  137:64, 
and  overwhelmingly  so  to  honey-bees,  85  of  which  visited  the  raspberry  and 
only  1  the  nine-bark.  Andrena  crataegi  was  the  only  bee  that  exhibited 
a  marked  preference  for  Opulaster,  the  ratio  being  46:7.  The  behavior  of 
the  flies  was  exactly  opposite  to  that  of  the  bees,  73  going  to  the  nine-bark 
and  one  to  the  raspberry.  This  appears  to  be  readily  explained  by  the 
fact  that  the  flowers  of  the  former  were  more  easily  seen  and  the  nectar 
more  accessible.  The  smaller  amount  of  nectar  and  the  ease  with  which 
it  can  be  obtained  make  clear  the  reason  why  the  bees  and  Apis  in  particular 
preferred  the  raspberry  with  its  less  conspicuous  flowers  and  larger  store 
of  nectar  less  accessible  to  flies. 

COMPETITION  OF  RUBUS  WITH  FRASERA,  CLEOME,  ETC. 

Comparison. — The  flowers  of  Jamesia  americana  resemble  those  of  the 
raspberry,  but  differ  in  forming  conspicuous  white  clusters  at  the  ends  of 
branches,  and  in  having  much  less  pollen  and  much  more  perfume.     Those 


98 


COMPETITION  AND  CONSTANCY. 


of  Cleome  serrulata  are  smaller,  pink  in  color,  and  grouped  in  conspicuous 
spike-like  racemes;  nectar  is  abundant,  but  the  odor  of  the  plant  is  strong. 
The  flowers  of  Geranium  richardsoni  are  white  and  occur  scattered  at  the 
ends  of  branches;  they  are  somewhat  larger  than  those  of  the  raspberry, 
but  contain  much  less  nectar  and  pollen.  Those  of  Chamaenerium  angusti- 
folium  are  about  the  same  size,  of  a  deep-pink  color  and  arranged  in  a  bril- 
liant raceme  often  2  or  3  feet  long;  the  value  in  both  nectar  and  pollen  closely 
approaches  that  of  the  raspberry.  The  single  flowers  of  Frasera  speciosa 
are  fairly  inconspicuous,  but  the  massive  spike-like  clusters  are  visible 
at  considerable  distances.  The  nectaries  are  highly  differentiated  and  the 
flow  abundant.  Mertensia  sibirica  differs  from  all  the  others  in  having 
tubular  flowers  of  a  blue  color;  they  produce  a  scanty  amount  of  pollen 
and  nectar  (plates  3,  7,  8,  and  10). 

Table  65. — Natural  and  bouquet  competition. 

Experiment  1,  \]4  hours,  10h30m  to  12  a.m.,  June  27. 
Experiment  2,  1  hour,  10h10m  to  llh10m,  July  6. 
Experiment  3,  1  hour,  8h30m  to  9h30m,  July  7. 
Experiment  4,  1  hour,  8h30m  to  9h30m,  July  7. 
Experiment  5,  1  hour,  9  to  10  a.m.,  July  12. 


Species. 

Plant,  R. 

strigosus. 

Plant, 
Opulaster. 

Species. 

Plant,  R. 
strigosus. 

Plant, 
Opulaster. 

First  experiment: 

Apis  mellifica 

Andrena  crataegi.  . 

madroni- 
tens 

vicina. .  .  . 
Bombus  bifarius. .  . 

proximus. . 

Osmia  bruneri 

Prosopis  elliptica.  . 

25 
0 

0 
2 
6 
2 
4 
3 
0 

0 
20 

1 
2 
0 
0 
0 
0 
7 

Third  experiment — 
Continued: 
Pseudomasaris 
vespoides 

1 

0 
0 

0 
41 

1 

Lepidoptera 

Total 

Fourth  experiment: 

Apis  mellifica 

Andrena  crataegi .  . 
Halictus  pulzenus. . 
Monumetha  albi- 

42 

Bouquet, 
R.  strigosus. 

4 
1 
0 

1 

0 
0 

50 

Plant, 
Opulaster, 

1 
3 
3 

0 

1 

9 

Total 

Second  experiment: 
Andrena  crataegi .  . 
Halictuspulzenus.  . 
Osmia  bruneri 

42 

Bouquet, 
R.  strigosus. 

6 

1 
1 

30 

Plant, 
Opulaster. 

18 

1 

0 
16 

Pseudomasaris  ves- 

Total 

Fifth  experiment: 

Apis  mellifica 

Andrena  crataegi.  . 
Bombus  bifarius. . . 

juxtus. . . . 

proximus. . 

Osmis  densa 

Prosopis  varifrons. . 

Total 

Total 

Third  experiment: 

Apis  mellifica 

Andrena  crataegi .  . 
Bombus  juxtus .... 
Megachile  wootoni. 

Osmia  bruneri 

densa 

6 

Plant,  R. 
strigosus. 

20 
0 
14 

1 
0 
3 

1 

17 

Opulaster 
in  vials. 

0 

1 
0 
0 
2 
1 
1 

9 

Plant,  R. 
strigosus. 

36 
0 
3 
0 
0 
2 

35 

Bouquet, 
Opulaster. 

0 
5 
0 

1 
2 
0 

39 

5 

RUBUS   STRIGOSUS. 


99 


Experiments. — In  the  first  case  all  three  plants  were  rooted  in  position, 
affording  a  test  of  natural  competition.  In  the  others,  Rubus  strigosus 
was  the  standard  and  its  competitors  were  arranged  in  bouquets  or  vials. 


Table  66 

. — Rubus  and  Frasera,  Cleome,  etc. 

Expt.  1,  1  hour,  11  to  12  a.m.,  June  23. 

Expt.  2,  2  hours,  10  to  12  a.m.,  July  13. 

Species. 

Plant,  R. 
strigosus. 

Plant,  M. 
sibirica. 

Plant,  J. 
americana. 

Species. 

Plant,  R. 

strigosus. 

Geranium 
in  vials. 

Bombus 

bifarius.  .  . 
Colletes 

oromontis . 

Diptera 

Total 

5 

0 
3 

1 

1 

4 

1 

0 

1 

15 
14 
2 
5 

0 
0 
0 
0 

proximus 

Prosopis  varifrons 

36 

0 

8 

6 

2 

26 

37 

1 

Chamae- 

nerium  in 

vials. 

0 

0 

0 

Prosopis  varifrons 

Total 

64 

0 

Expt.  3,  1  hour,  10  to  11  a.m.,  July  14. 

Expt.  4,  1  hour,  11  a.  m.,  to  12  m.,  July  18. 

Species. 

Plant,  R. 

strigosus. 

Bouquet,  F. 
speciosa. 

Species. 

Plant,  R. 
strigosus. 

Bouquet,  C. 
serrulata. 

Apis  mellifica 

57:62 
1:1 
0:0 
0:0 
1:1 
8:9 

11:16 
6:6 
2:2 
1:1 

37:62 
0:0 
2:5 
1:2 
3:3 
0:0 
2:2 
1:1 
4:4 
1:1 

22 
2 
0 

1 
0 
3 
4 
2 
3 

0 
1 

0 
1 
0 
0 
0 
0 

ronitens.  .  .  . 

Bombus  juxt> 
Colletes  ororc 

Halictus  pulzenus 

(Lasioglossum) 

ontis 

enus 

Megachile  wootoni 

Pseudomasaris  vespoides. . 

melanotricha 

Prosopis  elliptica 

Pseudomasaris  vespoides. . 

Total 

Protothyreopus  dilectus .  . 

Total . 

87:98 

51:80 

37 

3 

Summary. — The  total  number  of  visitors  to  Rubus  was  232,  in  contrast 
with  62  to  all  its  competitors,  though  the  raspberry  was  undoubtedly  favored 
by  being  the  plant  in  each  case.  With  the  flowers  in  vials,  Geranium  and 
Chamaenerium  exerted  no  competition  whatever  and  that  of  Cleome  was 
negligible.  Mertensia  approached  Rubus  in  attractiveness  and  Frasera 
apparently  exceeded  it,  as  suggested  by  the  relatively  greater  number  of 
visits  per  insect.     This  was  especially  true  of  the  honey-bee. 

RUBUS  STRIGOSUS  AND  TWO  OR  MORE  COMPETITORS. 

Comparison. — The  flowers  of  the  two  species  of  Pentstemon  are  much 
larger  than  those  of  the  raspberry,  but  they  contain  much  less  pollen  and 


100 


COMPETITION  AND  CONSTANCY. 


nectar.  P.  secundiflorus  possesses  a  pink-purple  corolla  with  a  wide  throat, 
while  that  of  P.  barbatus  is  a  flaming  scarlet  with  a  narrow  throat  and  hence 
excludes  the  larger  bees.  The  flowers  of  Scrophularia  nodosa  are  small 
and  of  a  dull  mottled  color,  but  these  disadvantages  are  offset  by  the 
abundant  nectar.  Those  of  Aquilegia  coerulea  are  large  and  showy,  the 
sky-blue  color  making  them  exceedingly  conspicuous;  they  contain  much 
pollen  and  nectar,  but  the  latter  is  unavailable  to  many  of  the  visitors. 
The  deep-blue  flowers  of  Mertensia  alpina  are  relatively  small,  with  a  narrow 
throat,  and  are  borne  in  small  clusters.  However,  they  possess  a  delightful 
fragrance,  which  is  indicated  by  their  local  name,  "forget-me-nots."  Table 
67  contains  the  record  for  1  hour  15  minutes,  from  10h45m  a.  m.  to  12  m.  on 
July  4,  and  table  68  for  an  hour,  10h20m  to  llh20m  a.  m.  on  July  12. 

Table  67. — Rubus,  Pentstemon,  and  Scrophularia. 


Species. 

Plant,  R. 
strigosus. 

Bouquet,  P. 
secundiflorus. 

Bouquet,  P. 
barbatus. 

Bouquet,  S. 
nodosa. 

Many. 
0:   0 
1:   4 
0:  0 
1:   2 
0:  0 
2:   5 
4:12 

1:  1 

1:   3 
0:   0 
4:12 
0:   0 
2:   3 
5:14 
4:   5 

0:   0 
0:   0 
0:   0 
0:  0 
0:   0 
0:   0 
0:   0 
0:   0 

0:   0 
1:  3 
0:   0 
0:  0 
0:   0 
0:   0 
0:   0 
4:21 

Total 

8:23 

17:38 

0:   0 

5:24 

Table  68. — Rubus,  Aquilegia,  and  Mertensia. 


Species. 


Plant,  R. 
strigosus. 


Bouquet,  A. 
coerulea. 


Bouquet,  M 
alpina. 


Apis  mellifica 

Andrena  crataegi 

madronitens 

Andronicus  sp 

Bombus  juxtus 

Halictus  pulzenus 

Megachile  texana 

Monumetha  albif rons 

Osmia  densa 

Prosopis  sp 

Pseudomasaris  vespoides 

Muscidae 

Atrytone  taxiles 

Total (Apis) 


Countless. 
1:    1 


16:20 


1:  1 

0:  0 

0:  0 

1:  1 
20:66 

7:  9 

1:  1 

1:  2 

0:  0 

0:  0 

0:  0 

4:  4 

1:  1 


36:85 


0:  0 
0:  0 
0:  0 
0:  0 
0:  0 
0:  0 
0:  0 
0:  0 
1:  1 
6:  6 
0:  0 
2:  2 
1:    1 


10:10 


Summary. — In  both  cases  the  honey-bees  were  so  numerous  that  they 
could  not  be  counted  at  the  same  time  that  the  other  visitors  were  noted. 
In  the  first  experiment  Pentstemon  secundiflorus  was  nearly  twice  as  attrac- 


RUBUS   DELICIOSUS — ROSA  ACICULARIS.  101 

tive  to  the  other  bees  as  the  raspberry  and  Scrophularia  was  about  equal  to 
the  latter.  It  is  interesting  that  P.  barbatus  received  neither  visits  nor 
inspections  from  bees  to  most  of  which  it  was  new,  but  this  probably  is  to 
be  ascribed  partly  to  color  and  partly  to  habit.  In  the  second  experiment 
the  honey-bee  was  again  almost  perfectly  constant  to  Rubus,  while  the  other 
bees  preferred  Aquilegia  in  the  ratio  of  2:1.  Bombus  juxtus  showed  a 
decisive  preference  for  the  latter,  as  Prosopis  did  for  Mertensia;  on  the 
contrary,  the  wasp  Pseudomasaris  went  only  to  the  raspberry.  Taking  all 
bees  into  account,  Rubus  was  much  the  most  attractive,  but,  ignoring  the 
honey-bee,  the  attractive  features  of  Pentstemon  secundifiorus  and  Aquilegia 
coerulea  proved  more  potent  than  the  control  exerted  by  habit. 

RUBUS  DELICIOSUS. 

Experiments. — In  the  studies  with  this  species  it  was  compared  with 
two  plants  of  the  same  family,  viz,  Rosa  acicularis  and  Prunus  demissa. 
The  flower  of  the  rose  resembles  that  of  the  salmonberry  closely  in  form, 
size,  and  grouping,  but  contrasts  sharply  in  color.  On  the  other  hand, 
the  flowers  of  the  chokecherry,  though  white,  are  several  times  smaller 
and  arranged  in  close  racemes.  The  color  area  is  much  the  same  in  the 
three,  but  in  Prunus  it  is  broken  by  the  spaces  between  the  flowers;  the 
raceme  is  much  the  most  fragrant  and  produces  more  nectar,  while  the 
amount  of  pollen  appears  to  be  much  the  same  as  in  the  single  flowers  of 
the  other  two  species.  Since  the  plants  grew  in  juxtaposition,  it  was  only 
necessary  to  bring  the  branches  together  to  form  an  effective  competition 
group,  though  in  the  last  case  a  bouquet  of  Rubus  was  used  (table  69). 

Summary. — Of  the  total  of  434  visitors,  302  went  to  Prunus,  120  to 
Rubus,  and  12  to  Rosa.  While  this  indicates  the  relative  attractiveness, 
it  must  be  considered  with  reference  to  the  fact  that  387  of  the  total  were 
contributed  by  Andrena  and  Diptera.  Had  either  Apis  or  Bombus  been 
abundant  in  the  area  at  this  time,  the  results  would  have  been  very  different. 
The  marked  preference  of  Andrena  for  Prunus  is  shown  by  the  fact  that 
the  latter  obtained  225  visitors  to  43  for  Rubus  and  4  for  Rosa,  all  of  the  four 
species  exhibiting  the  same  behavior.  The  preference  was  less  marked  in 
the  case  of  the  flies,  75  going  to  Prunus  and  40  to  Rubus.  The  honey-bee 
was  all  but  perfectly  constant  to  Rubus,  26  visiting  this  in  contrast  to  one 
to  Rosa  and  none  to  Prunus.  All  told,  the  rose  received  less  than  a  tenth  of 
the  total  number  of  visitors  in  the  experiments  concerned,  affording  clear-cut 
evidence  of  the  effect  of  habit  in  the  face  of  greater  total  attraction. 

ROSA  ACICULARIS 

Comparison. — Of  the  competitors  employed,  Rubus  deliciosus  most 
nearly  resembles  the  rose  in  size  and  form,  but  contrasts  sharply  with 
its  white  color.  Rubus  strigosus  and  Opulaster  opulifolius,  though  likewise 
belonging  to  the  same  family  and  white  in  color,  differ  greatly  in  form,  size, 
and  arrangement.  Geranium  caespitosum  and  Chamaenerium  angustifolium 
approach  closely  in  color,  but  they  are  much  smaller  and  yield  much  less 
pollen,  and  this  is  largely  true  also  for  Cleome  serrulata.  Aquilegia  coerulea 
equals  the  rose  in  pollen  production  and  excels  it  in  the  attractiveness  of  the 
bright  blue  corolla,  while  the  flowers  of  both  species  of  Mertensia  are  rela- 


102 


COMPETITION  AND  CONSTANCY. 


tively  small  and  produce  little  pollen,  but  are  readily  visible  by  virtue  of 
their  deep  blue  color  (plates  3,  7,  8,  and  11). 

Table  69. — Rubus,  Rosa,  and  Prunus. 


Expt.  1.2  hours,  9h45m  to  llh45ma.m.June23. 

Expt.  3,  1  hour,  10  to  11  a.m.,  June  28. 

Species. 

oq 

3 
.    B 

c  ® 

s 

Species. 

| 

tf  .2 

o 

03  13 
S 

W   3 
-w   ° 

a  "3 

03    03 

03 

3    oj 
03 -O 

First  experiment: 

Andrena  madronitens .... 
prunorum 

0 
0 
5 
3 
21 

7 
4 

25 
0 

45 

Andrena  crataegi 

madronitens.  .  .  . 

10 
0 
0 
0 
0 

1 

0 

1 

3 
0 
1 
2 
1 
0 
1 
0 

85 
2 
2 
1 
0 
0 
0 
3 

proximus 

Total 

29 

81 

Total 

12 

8 

93 

Two  hours,  8h30m  to  10h30m  a.m.,  June  25. 

6 
1 
6 
1 
0 
5 

22 
6 

12 
0 
1 

23 

madronitens 

Expt.  4,  2  hours,  9h48m  to  lh48m  a.m.,  July  3. 

Pseudomasaris  vespoides .  .  . 

Species. 

o 

3 

tf.2 
.  o 

a  • 

OJT3 

W    3 

03    03 

Total 

19 

64 

Expt.  2,  1  hour,  10  to  11  a.m.,  June  28. 

Species. 

« i 

23 
2 
2 
1 

2 
1 
1 
3 
4 
3 
1 

1 

1 

2 
0 
0 
0 
0 
0 
0 
0 
0 

..    03 

3  .2 

05 

Halictus  pulzenus 

Pseudomasaris  vespoides  . 

13 

2 
1 

1 

54 
6 
0 
4 

Anthrax  lateralis 

Eristalis  latifrons 

Syrphus  americanus 

Systoechus  vulgaris 

madronitens 

Total 

Total 

17 

64 

43 

4 

Experiments. — In  order  to  save  space  some  of  the  less  important 
details  of  installation  are  omitted  and  others  are  given  in  the  discussion 
that  follows  tables  70  and  71.  As  always,  an  equal  number  of  flowers  was 
used  as  a  rule  or  an  endeavor  was  made  to  have  the  attractive  surfaces  equal. 

Summary. — Rosa  acicularis  proved  to  be  less  attractive  than  its  com- 
petitors   taken    collectively,    the    ratio    being    327:420.     Rubus    strigosus 


ROSA   ACICULARIS. 
Table  70. — Rosa,  Rubus,  Geranium,  etc. 


103 


Expt.  1,  1  hour,  8h45m  to  9h45m  a.m.,  July  6. 



Expt.  3,  1  hour,  8h50m  to  9h50m  a.m.,  July  6.   ■ 

Species. 

Plant,  R. 
strigosus. 

Bouquet,  R 
acicularis. 

Species. 

Bouquet,  R 
acicularis. 

Plant,  O. 
opulifoliua. 

50 
1 
2 
1 
0 
3 
4 
0 
0 

3 

0 
0 
0 

1 

5 
0 
2 
1 

Andrena  crataegi 

madronitens.  .  .  . 

Halictus  pulzenus 

Prosopis  varifrons 

0 
0 
0 
0 
0 

20 
1 
2 
1 

26 

Andrena  crataegi 

Halictus  pulzenus 

Osmia  coloradella 

Pseudomasaris  vespoides. . 

Total 

0 

50 

Expt.  4,  \y2  hours,  9h30m  to  11  a.m.,  July  8. 

Total 

61 

12 

Species. 

Plant,  R. 
acicularis. 

Plant,  G. 
caespitosum. 

Expt.  2,  1  hour,  10h40m  to  llh40m  a.m.,  July  7. 

Species. 

Plant,  R. 

strigosus. 

Bouquet,  R. 
acicularis. 

Prosopis  episcopalis 

elliptica 

10:10 
0:0 
1:1 
9:15 
1:4 
9:30 
4:13 
4:15 
4:4 
1:1 
1:1 
5:11 
4:9 
5:16 
1:1 
1:1 
5:5 

33:36 
2:2 
0:0 
0:0 
0:0 
0:0 
0:0 
0:0 
1:1 
8:8 
0:0 
0:0 
0:0 
0:0 
0:0 
0:0 
0:0 

42 
1 
2 
2 
5 
0 

0 
0 
4 
0 
0 
2 

Andrena  crataegi 

occidentalis 

Anthophora  simillima.  .  .  . 
Halictus  (Evylaeus)  sp.. .  . 

pulzenus 

( Lasioglossum )  sp. 

Megachile  texana 

wootoni 

Monumetha  albifrons.  .  .  . 

Megachile  wootoni 

Pseudomasaris  vespoides. . 

Total 

52 

6 

Expt.  3,  1  hour,  10h40m  to  llh40m  a.m.,  July  7. 

sp 

Species. 

Bouquet,  R. 
strigosus. 

Plant,  R. 
acicularis. 

Eristalis  latifrons 

Total 

65:137 

44:47 

Anthophora  simillima .... 
Apis  mellifica 

2 
0 
1 
1 
1 
2 

0 
4 
1 
0 
0 
0 

Expt.  5,  2  hours,  10h05m  to  12h05m  a.m.,  July  18. 

Halictus  (Evylaeus)  sp. .  . 
Monumetha  albifrons .... 

Species. 

Plant,  R. 
acicularis. 

Bouquet,  C. 
serrulata. 

Syrphus  americana 

Total 

8:15 

0:0 

5:6 

1:1 

1:1 

1:4 

1:1 

2:2 

1:3 

7 

5 

15:22 
1:4 
2:2 
0:0 
2:3 
1:2 
0:0 
5:8 
0:0 

occidentalis 

Andrena  madronitens.  .  .  . 

Prosopis  elliptica 

Megachile  wootoni 

Syrphus  americanus 

Total 

26:41 

20:33 

104 


COMPETITION  AND  CONSTANCY. 
Table  71. — Rosa,  Chamaenerium,  Aquilegia,  etc. 


Expt.  1,  IK  hours,  10h30m  a.m.  to  12  m.,  July  11.         Expt.  4,  1)4  hours,  S^O™  to  10  a.m.,  July  12. 

Species. 

Plant, 

R. 

acicularis. 

Vials, 

C. 
angusti. 

Species. 

Plant,  R. 
acicu- 
laris. 

Bouquet, 

A.  coer- 

ulea. 

Bouquet, 
M.  al- 
pina. 

5 

2 
0 
1 
1 

0 
0 

1 
0 
0 

Adrena  crataegi 

madronitens.  .  . 

1:1 
2:2 
4:4 
1:1 
12:16 
1:1 
1:1 
2:2 
1:1 
0:0 
7:7 

0:0 
5:5 
2:5 
0:0 

29:61 
0:0 
4:5 
1:1 
0:0 
1:1 

11:11 

0:0 
1:1 
0:0 
0:0 
0:0 
1:1 
0:0 
0:0 
0:0 
2:2 
3:3 

Bombus  occidentalis .  .  . 

juxtus 

Halictus  pulzenus 

Monumetha  albifrons .  . 

Prosopis  basalis 

Anthrax  lateralis 

Eristalis  arbustorum .  .  . 
Muscidae 

Total 

Total 

9 

1 

Expt.  2,  1^  hours,  lO^O™  a.m.  to  12  m.,  July  12. 

Species. 

Plant, 
Rosa. 

Vials, 
Rosa. 

Vials, 
Chamae. 

32:36 

53:89 

7:7 

Expt.  5,  1  hour,  8h30m  to  9h30m  a.m.,  July  20. 

Bombus  proximus 

bifarius 

juxtus 

Halictus  pulzenus 

man'tonellus.. 
Megachile  wootoni .... 

Total 

72 
2 

1 
3 
1 
1 

41 
2 

1 
1 
1 
0 

7 
0 
0 
0 
0 
0 

Species. 

Bouquet, 
Rosa. 

Bouquet, 
Aquil- 
legia. 

Bouquet, 
Rubus  d. 

80 

46 

7 

0:0 

7:9 

23:31 

5:17 

2:10 

5:6 

0:0 

10:14 

11:11 

2:2 

1:1 
0:0 
13:25 
0:0 
1:1 
3:3 
1:2 
1:1 
1:1 
0:0 

0:0 
0:0 
6:7 
0:0 
0:0 
2:2 
0:0 
3:3 
1:1 
0:0 

Andrena  crataegi 

Bombus  juxtus 

occidentalis.  .  . 
Clisodon  terminalis .... 

Halictus  pulzenus 

Monumetha  albifrons .  . 
Prosopis  basalis 

elliptica 

Expt.  3,  3  hours,  7h30m  to  10h30m  a.m.,  June  27. 

Species. 

Plant,  R. 
acicularis. 

Plant,  M. 
sibirica. 

0 
3 

2 
9 
0 
5 
0 
1 
2 

23 
0 
0 
1 
1 
0 

60 
0 
0 

Total 

65:100 

21:34 

12:13 

Total 

22 

85 

greatly  exceeded  it  in  attractive  power,  in  the  ratio  of  120:23,  though  this 
was  due  chiefly  to  the  habitual  preference  of  the  honey-bee.  When 
Rosa  was  the  standard  and  Rubus  the  bouquet,  the  difference  was  slight, 
owing  to  the  fact  that  Apis  then  visited  the  first  alone.  In  competition 
with  Opulaster,  the  rose  received  no  visitors,  a  consequence  explained  by  the 
fact  that  practically  all  the  visitors  present  were  flies  and  species  of  Andrena. 
The  rose  was  most  effective  in  competition  with  flowers  of  similar  color 
but  smaller  size,  the  ratio  being  65 :  44  for  Geranium,  26 :  20  for  Cleome.  and 


GERANIUM. 


105 


9:1  for  Chamaenerium.  When  a  flower  of  rose  or  of  fireweed  in  a  vial  was 
paired  with  rose  flowers  on  the  bush,  the  latter  yielded  85  visitors  to  49  for 
the  first  and  7  for  the  second.  When  Rosa  as  the  standard  competed  with 
Aquilegia,  the  latter  received  nearly  twice  as  many  visitors  and  more  than 
twice  as  many  visits,  but  when  both  were  in  the  form  of  bouquets,  the  num- 
ber of  visitors  and  visits  to  the  rose  was  thrice  as  great.  This  exception  to 
the  general  rule  for  standard  and  bouquet  was  due  chiefly  to  the  reversal 
of  the  behavior  of  Bombus  juxtus  and  the  greater  abundance  of  Prosopis. 
The  success  of  Mertensia  sibirica  in  securing  nearly  four  times  as  many 
visitors  as  the  rose  was  the  result  of  the  constant  preference  of  Andrena 
madronitens  and  Osmia  phaceliae  for  it,  all  the  other  species  choosing  the  rose. 
The  small  number  of  visitors  for  Mertensia  alpina  is  partly  to  be  explained 
by  its  being  removed  a  long  distance  from  its  native  habitat  in  terms  of 
climate  and  vegetation. 

Competition  with  normal  and  mutilated  Aquilegia. — In  this 
experiment  were  employed  50  normal  flowers  of  the  rose  and  columbine, 
and  10  flowers  of  each  of  the  three  kinds  of  mutilation.  In  addition,  a 
pile  of  loose  petals  6  inches  in  diameter  was  placed  on  the  ground.  The 
period  of  observation  was  one  hour,  9h15m  to  10h15m,  July  13. 

Table  72. — Competition  of  Rosa  with  normal  and  mutilated  Aquilegia. 


Species. 

Normal. 

Mutilations. 

Plant, 
Rosa. 

Bouquet, 
Aquilegia. 

Sepals  and 
petals  off. 

Petals 
off. 

Petals  and 
spurs  off. 

Loose 
petals. 

Bombus  juxtus 

occidentalis .  .  . 

Andrena  crataegi 

Halictus  pulzenus 

Megachile  texana 

w.  calogaster 
Monumetha  albifrons .  . 

Osmia  densa 

Prosopis  elliptica 

5 
6 
9 
0 
0 
5 
1 
1 
1 
0 
0 
0 

5 
9 
10 
0 
0 
5 
1 
1 
1 
0 
0 
0 

28:31 
1:   1 
0:   0 
1:    1 
1:    1 
0:   0 
1:   1 
0:   0 
0:   0 
0:   0 
1:    1 
1:    1 

7:10 
0:   0 
0:   0 
0:   0 
0:    0 
0:   0 
0:    0 
0:   0 
0:   0 
0:   0 
0:    0 
0:   0 

6:   6 
0:   0 
1:    1 
0:   0 
0:   0 
0:   0 
0:   0 
0:   0 
1:    1 
1:    1 
1:    1 
1:    1 

5:6 
0:0 
0:0 
0:0 
0:0 
1:1 
0:0 
0:0 
0:0 
0:0 
0:0 
0:0 

2:2 
0:0 
0:0 
0:0 
0:0 
0:0 
0:0 
0:0 
0:0 
0:0 
0:0 
0:0 

Syrphus  americanus. . .  . 
Muscidae 

Total 

28:32 

34:37 

7:10 

11:11 

6:7 

2:2 

While  the  rose  was  more  attractive  to  Bombus  occidentalis,  Andrena 
crataegi  and  Megachile  w.  calogaster,  the  greater  number  of  visitors  of 
B.  juxtus  gave  the  preference  to  the  columbine.  The  mutilations  were 
relatively  more  visited  than  the  normal  flowers,  this  exception. to  the  rule 
for  decorollate  flowers  being  explained  by  the  bright-colored  stamen  mass 
and  the  blue  color  of  the  sepals. 

GERANIUM. 

Comparison. — The  flowers  of  Geranium  caespitosum  and  G.  richardsoni 
are  almost  identical  except  for  the  color,  the  former  being  pink-purple  and 


106  COMPETITION  AND  CONSTANCY. 

the  latter  practically  white.  In  nature,  G.  caespitosum  is  much  more  visited, 
as  it  is  a  plant  of  open  sunny  slopes.  Its  flowers  are  larger  and  much  more 
conspicuous  than  those  of  Rubus  strigosus,  but  are  only  about  one-fourth 
the  size  of  the  rose.  They  are  also  much  smaller  than  the  flowers  of  Aqui- 
legia  coerulea  and  the  color  somewhat  less  attractive,  while  the  pollen  is 
much  less  abundant.  Mertensia  alpina  possesses  the  advantage  of  blue 
flowers,  but  the  cluster  is  rather  less  conspicuous  than  a  single  geranium. 
In  the  group  of  natural  competitors,  the  heads  of  Aster  bigelovi  resemble 
the  flowers  of  geranium  in  size  and  color,  but  they  yield  more  nectar  and 
pollen.  Campanula  rotundifolia,  in  spite  of  its  deep  blue  color,  produces 
little  pollen  or  nectar  and  moot  pollinators  ignore  it.  In  both  Allium 
recurvatum  and  Heracleum  lanatum,  the  smallness  of  the  flowers  is  com- 
pensated by  their  grouping  in  umbels,  though  even  this  is  little  effective 
in  Heracleum.  The  pink  flowers  of  Allium  produce  an  amount  of  nectar 
and  pollen  that  is  out  of  proportion  to  their  size.  Of  the  competitors 
with  zygomorphic  flowers,  Pentstemon  secundiflorus  and  P.  barbatus  have 
larger  and  more  brilliant  flowers,  and  the  cluster  is  larger  and  more  vivid 
in  Castilleia  miniata,  while  the  chief  asset  of  the  small,  dull  flowers  of 
Scrophularia  nodosa  lies  in  the  abundant  nectar  (plates,  3  7,  11,  12,  13, 
and  14). 

Experiments. — Table  73  deals  with  the  competition  between  the  two 
species  of  Geranium  in  various  installations,  table  74  with  competition  be- 
tween Geranium  and  other  genera,  and  tables  75,  76,  and  77  with  group 
competition. 

Although  Geranium  caespitosum  yielded  277  visitors  to  155  for  G.  richard- 
soni,  in  competition  with  each  other,  they  are  more  nearly  equal  in  attrac- 
tiveness than  this  would  indicate.  This  difference  is  more  than  accounted 
for  in  the  behavior  of  Prosopis,  which  preferred  caespitosum  in  the  ratio  of 
184:28,  chiefly  when  this  species  was  the  standard.  The  two  were  practi- 
cally equal  when  both  were  used  in  the  form  of  bouquets,  and  they  changed 
rank  in  two  successive  periods  in  which  they  alternated  as  standards,  the 
respective  ratios  being  88:9  and  83:10.  This  equality  is  further  indicated 
by  their  behavior  in  competition  with  Rubus  strigosus,  though  the  conditions 
were  not  precisely  comparable  in  the  different  experiments.  When  plants 
were  compared,  A  pis  was  perfectly  constant  to  the  raspberry,  but  in  all 
other  cases  it  exhibited  a  practically  exclusive  preference  for  the  standard 
plant,  going  to  richardsoni,  caespitosum,  or  strigosus  as  each  took  this  role. 
Between  richardsoni  and  strigosus  as  plants,  Prosopis  gave  a  ratio  of  42:1, 
while  between  bouquets  of  G.  caespitosum  and  Rosa  the  ratio  was  28:0. 
The  honey-bee  behaved  similarly  in  the  latter  choice,  while  for  Bombus  the 
preference  was  reversed,  namely,  0:29,  as  it  was  likewise  for  Megachile 
and  Anthophora.  However,  Aquilegia  in  a  mixed  boquet  was  as  attractive 
as  standard  G.  caespitosum,  while  the  associated  Mertensia  alpina  received 
but  one  visit.  It  is  interesting  to  note  that  Andrena  crataegi  was  the  only 
visitor  to  both  Geranium  and  Aquilegia  in  this  experiment. 

The  size  of  the  flowers  differs  so  much  in  this  group  that  exact  comparisons 
are  difficult.  In  spite  of  the  size  of  the  clusters,  however,  the  pinkish  or 
white  flowers  of  Allium  and  Heracleum  were  obviously  at  a  disadvantage. 
The  flowers  of  Geranium  and  Campanula  and  the  heads  of  Aster  are  somewhat 


GERANIUM.  107 

Table  73. — Competition  of  Geranium  caespitosum  and  G.  richardsoni. 


1 

Expt.  1,1%  hours,  lO^O"  a.m.  to  12  m.,  July  14. 

Expt.  4,  2  hours,  8  to  10  a.m.,  July  9. 

Species. 

Plant, 
caespitosum. 

Bouquet, 
richardsoni. 

Species. 

Caespitosum, 
vials. 

Richardsoni, 

plant. 

Andrena  madronitene . . . 

Halictus  pulzenus 

Megachile  wootoni 

Monumetha  albifrons. . . 

Prosopis  elliptica 

varifrons 

0 

14 

5 

3 

46 

57 

1 

2 

5 
0 
0 
0 
3 
7 
0 
0 

0 
2 
2 
0 
5 
0 

49 
2 

15 
3 

18 

1 

Andrena  madronitens .  . 

Bombus  bifarius 

proximus 

Halictus  pulzenus 

Prosopis  varifrons 

Total 

9 

88 

128 

15 

2  hours,  10  a.m.  to  12  m.,  July  9. 

Exp.  2,  half-hour,  9h25m  to  9h56m  a.m.  July  14. 

Apis  mellifica 

0 
1 
0 
1 
1 
0 

1 
3 
1 
1 
1 
1 

Vials 

Vials 

Halictus  pulzenus 

Osmia  phaceliae 

Prosopis  elliptica 

5 
1 
0 

13 
1 

55 
6 
1 
2 

0 
0 

1 
0 
0 
6 
2 
0 
1 

Anci  trocerus  sp 

Bombus  juxtus 

Halictus  pulzenus 

Monumetha  albii'rons.  . 

Prosopis  elliptica 

varifrona 

Sphex  vulgaris 

Total 

3 

8 

Expt.  3,  half-hour,  8h45m  to  9h15m  a.m.  August  5. 

Species. 

Bouquet, 
caespitosum. 

Bouquet, 
richardsoni. 

Total 

83 

10 

Bombus  bifarius 

Foenus  perplexus 

Halictus  pulzenus 

(Chloralictus) 

2 
2 

8 

1 

4 
0 
1 
2 

5 
0 
5 

1 

4 
1 
0 
5 

2  hours,  1  to  3  p.m.,  July  9. 

Andrena  madronitens.  . 
Ancistrocerus  sp 

7 
6 
1 
2 
5 
12 
1 

7 
2 
0 
2 
1 
2 
0 

(Lasioglossum) 
sp 

Osmia  penstemonis  .... 

Prosopis  elliptica 

wootoni 

Total 

Megachile  relativa 

Prosopis  elliptica 

varifrons 

Protothyreopus  dilectus 

Total 

20 

21 

34 

14 

Expt.  6,  1  hour,  S^O00  to  9h30m  a.m.,  July  23. 

Species. 

Plant, 
caesp. 

Bouquet 

caesp. 

richard. 

1 

1 

1 

1 
2 
2 

1 
0 
0 

1 
0 
0 

0 
1 
0 

1 
0 
0 

Andrena  madronitens  . . 
Bombus  occidentalis .  .  . 
Halictus  (Lasioglossum) 

sp 

pulzenus 

Prosopis  varifrons 

Total 

8 

2 

2 

108 


COMPETITION  AND  CONSTANCY. 


Table  74. — Geranium,  Rubus,  Rosa,  Aquilegia,  etc 

Expt.  1,  1  hour,  O^O"  to  lO^O*  a.m.,  July  2. 

Expt.  3,  1  hour,  2h50m  to  3h50m  p.m.,  July  11. 

Species. 

Plant,  G. 
richard. 

Plant,  R. 
strigosus. 

Species. 

Mixed  bouquet. 

Ger.  caes. 

Rosa  acic. 

0 
0 
1 
1 

40 
2 

1 

1 
1 
1 

29 
1 
0 
0 
1 
0 

0 
0 
0 
0 

16 
15 
13 
0 
0 
0 
0 
2 
0 
0 
3 
1 

0 
0 
0 
8 
21 
8 
3 
0 
1 
1 
0 
0 

Andrena  madronitens .  . 
Osmia  bruneri 

Prosopis  basalis 

elliptica 

Bombus  occidentalis . . . . 

juxtus 

Megachile  wootoni 

Anthophora  simillima. .  . 

Prosopis  basalis 

elliptica 

Psammophila    violace- 

Sphex  vulgaris 

Andrena  crataegi 

prunorum 

Osmia  melanotricha .  .  .  . 
Halictus  pulzenus 

48 

31 

50 

42 

Expt.  2,  1  hour,  11  a.m.  to  12  m  ,  July  10. 

Expt.  4,  half-hour,  ll^O™  a.m.  to  12  m.,  July  12. 

Species. 

Plant,  G. 
caespitosum. 

Bouquet,  R. 
strigosus. 

Species. 

Plant,  G. 
caesp. 

Mixed  bouquet. 

11 

2 
0 
0 

0 
0 

1 
1 

Halictus  pulzenus 

A.  coer. 

M.  alp. 

Prosopis  basalis 

Total 

13 

2 

Andrena  crataegi 

madronitens.  . 

0:0 
3:3 
0:0 
0:0 
0:0 
0:0 
0:0 
1:1 

1:1 
1:1 
1:1 
4:4 
2:2 

1:   1 
1:   1 
1:   1 
1:   1 
2:   2 
4:   4 
1:    1 
0:   0 

0:   0 
0:   0 
0:   0 
0:   0 
0:   0 

0:0 
0:0 
0:0 
0:0 
1:1 
0:0 
0:0 
0:0 

0:0 
0:0 
0:0 
0:0 
0:0 

1  hour,  11  to  12,  July  11. 

Bombus  juxtus 

occidentalis.  .  . 

Halictus  pulzenus 

Monumetha  albifrons .  . 
Prosopis  episcopalis .... 
Protothryreopus  dilec- 

48 
2 
0 
0 

0 
0 
1 

1 

Halictus  pulzenus 

Prosopis  basalis 

Total 

50 

2 

Arctophila  flagrans.  .  .  . 

Eristalis  latifrons 

Symmorphus  sp 

Syrphus  americanus. .  .  . 

Total ' 

1  hour,  10  to  11  a.m.,  July  8. 

Species. 

Bouquet,  G. 
caespitosum. 

Plant,  R. 
strigosus. 

13:13 

11:11 

1:1 

0 
4 

1 
1 

24 
0 
1 
1 

Ancictrocerus  sp 

Prosopis  basalis 

Total 

6 

26 

GERANIUM. 


109 


similar  in  color  and  size.  As  there  were  25,  10,  and  5  respectively,  the 
corresponding  numbers  for  visitors  and  visits  are  11:26,  45:90,  and  10:10, 
the  much  larger  nectar  supply  of  Aster  giving  it  a  great  advantage. 

Table  75. — Natural  competition:  Geranium,  Aster,  Allium,  Campanula,  Heracleum. 


1  hour,  10h15m  a.m.  to  llh15m  a.m.,  August  2. 

Species. 

G.  caesp- 
itosum. 

A.    big- 
elovi. 

A.  recur- 
vatum. 

C.  rotund- 
ifolia. 

H.  lan- 
atum. 

0:   0 
1:   1 
1:   2 
1:    1 
6:11 
2:11 
0:    0 
0:    0 
0:   0 
0:   0 

1:   2 

0:   0 
0:   0 
0:   0 
2:   2 
0:   0 
4:   4 
3:   7 
3:   8 
6:14 

0:   0 
0:    0 
2:   4 
0:    0 
0:   0 
0:    0 
0:   0 
0:   0 
0:   0 
0:   0 

0:    0 
0:   0 
0:   0 
0:   0 
0:   0 
0:   0 
2:   2 
0:   0 
0:   0 
0:   0 

0:   0 
0:   0 
0:   0 
0:   0 
0:   0 
0:   0 
0:   0 
0:   0 
1:    1 
0:    0 

Total 

11:26 

19:37 

2:  4 

2:   2 

1:    1 

Summary. — In  these  two  experiments  the  preferences  of  most  of  the 
visitors  were  so  pronounced  that  the  usual  difference  between  plant  and 
bouquet  is  hardly  to  be  seen.  Anthophora,  Bombus,  and  Osmia  were  the 
only  visitors  to  work  on  both  standard  and  bouquet,  the  first  two  giving 
preference  to  the  rose  and  the  last  to  Pentstemon  secundiflorus.  Andrena 
and  Megachile  likewise  preferred  the  rose,  while  Apis  selected  Geranium. 
The  competition  between  Geranium  and  Castilleia  was  conclusive  as  to  the 
marked  specialization  of  the  latter,  the  broad-tailed  humming-bird  being 
the  regular  pollinator  and  Osmia  the  only  insect  to  visit  it.  As  in  former 
experiments,  Pentstemon  barbatus  was  entirely  ignored,  perhaps  because  of 
its  narrow  vermilion  corolla,  and  the  difference  between  P.  secundiflorus 
and  Scrophularia  was  less  than  would  be  expected  from  the  size  and  color 
of  the  former.  In  both  experiments  more  individuals  of  Pseudomasaris 
went  to  Scrophularia,  but  they  made  a  larger  number  of  visits  to  Pentstemon. 
Osmia,  however,  showed  an  all  but  exclusive  preference  for  the  latter. 
In  the  second  experiment  the  bouquet  was  later  turned  so  that  the  flowers 
of  P.  barbatus  were  in  the  position  formerly  occupied  by  Scrophularia. 
Pseudomasaris  returned  to  the  original  position  of  the  latter,  recognized 
its  mistake,  and  then  flew  through  the  red  flowers  of  the  Pentstemon  to  the 
figwort.  Andrena  crataegi  flew  7  times  within  0.5  cm.  of  Scrophularia 
and  4  times  around  P.  secundiflorus,  but  ignored  P.  barbatus;  it  then  flew  to 
Rosa  and  alighted. 

Since  there  were  four  times  as  many  roses  and  twice  as  many  castilleias 
as  geraniums,  the  latter  was  relatively  as  attractive  as  the  others,  receiving 
more  visitors  but  fewer  visits  than  the  rose.  The  three  species  in  the 
bouquet  were  represented  by  an  equal  number  of  spikes.  Pentstemon 
secundiflorus  was  about  50  per  cent  more  attractive  than  Scrophularia, 
probably  owing  to  its  much  larger  size  and  brilliant  color. 


110 


COMPETITION  AND  CONSTANCY. 


The  results  are  interesting  only  in  showing  the  behavior  of  Bombus 
juxtus  on  two  successive  and  similar  mornings.  On  the  first  the  bouquet 
of  Chamaenerium  approached  the  Geranium  plant  in  attraction,  but  there 
was  a  great  discrepancy  on  the  second  day.  Monarda  received  a  few 
visits  on  one  and  inspections  only  on  the  other,  in  spite  of  the  fact  that 
B.  juxtus  can  reach  the  nectar  when  it  chooses.  Gilia  was  not  even  inspected, 
the  visitors  evidently  knowing  that  the  nectar  is  inaccessible  to  them. 

Table  76. — Plant  and  bouquet  competition  of  several  species. 


Expt.  1,  2  hours,  8  to  10  a.m.,  July  3. 


Species. 


Plant. 


Geranium        Rosa 


Mixed  bouquet. 


Pent.  sec.  Pent.  barb.  Scroph.  nod 


Andrena  crataegi 

madronitens.  .  . 

prunorum 

Anthophora  simillima .  .  . 

Apis  mellifica 

Bombus  juxtus  (worker) , 
(queen) . . 

occidentalis 

Colletes  sp 

Megachile  w.  calogaster . 

Osmia  sp 

Prosopis  episcopalis.  .  .  . 
Peeudomasaris  vespoides 

Total 


0:  0 
0:  0 
0:  0 
0:  0 
9:27 
0:   0 


0:  0 
1:  1 
0:   0 


0:  0 
0:  0 
0:  0 
1:  2 
0:  0 
1:    1 


0:   0 
0:   0 


0:   0 
0:   0 


0:  0 
0:  0 
2:10 
0:  0 
5:59 


0:  0 
0  0 
0:   0 


0:  0 
1:  7 
0:  0 
0:  0 
1:  1 
0:  0 
8:54 


13:34 


31:156 


0:   0 


10:62 


Expt.  2,  2  hours,  10  a.m.  to  12  m.,  July  3. 


Species. 


Geranium 


Castilleia 


Mixed  bouquet. 


Apis  mellifica 

Bombus  juxtus 

Osmia   melanotricha .  .  . 
pentstemonis . . . 

Prosopis  elliptica 

Pseudomasaris  vespoides 

Vespid 

Selasphorus  platycercus . 

Total 


6:16 
1:  1 
0:  0 
0:  0 
1:  2 
0:  0 
0:  0 
0:   0 


0:  0 

0:  0 

0:  0 

1:  2 

0:  0 

0:  0 

0:  0 
19:39 


0:  0 
0:  0 
6:19 
6:21 
0:  0 
6:75 
0:  0 
0:   0 


8:19 


20:41 


18:115 


0:  0 
0:  0 
0:  0 
0:  0 
0:  0 
0:  0 
0:  0 
0:   0 


0:   0 


0:  0 
0:   0 

0:  0 
0:  0 
0:  0 
8:39 
2:  9 
0:   0 


10:48 


CHAMAENERIUM  ANGUSTIFOLIUM. 

Comparison. — The  flowers  of  Geranium  caespitosum  resemble  those  of 
the  fireweed  in  form  and  color,  but  are  somewhat  larger.  Perhaps  the 
chief  difference  between  them  lies  in  the  fact  that  they  are  scattered  in 
the  one  and  grouped  in  a  conspicuous  raceme  in  the  other.  The  fireweed 
produces  more  nectar,  and  the  pollen  is  not  only  more  abundant  but  is  also 


PENTSTEMON. 


Ill 


available  in  each  flower  for  a  much  longer  period.  Both  Aconitum  colum- 
bianum  and  Delphinium  scopulorum  afford  a  striking  contrast  to  the  fireweed 
in  the  form  and  color  of  the  flower.  The  blue  or  purple  color  and  the  great 
abundance  of  pollen  would  seem  to  make  them  more  attractive,  but  this  is 
offset  by  the  more  constant  flow  of  nectar  in  Chamaenerium.  Frasera 
speciosa  is  similar  to  the  latter  in  the  form  and  size  of  the  flower,  but  the 
corolla  is  dull  green.  It  would  seem  to  be  greatly  handicapped  by  the 
color  and  the  small  number  of  stamens,  but  the  nectar  is  abundant  and 
apparently  very  palatable,  a  fact  that  more  than  compensates  for  the 
larger  size,  brighter  color  and  more  abundant  pollen  of  Aquilegia  coerulea 
(plates  2,  7,  8,  and  10). 

Table  77. — Plant  and  bouquet  competition  of  several  species. 


Expt.  1,  1  hour,  47  minutes,  8h10m  to  9h57m  a.m.,  August  15. 

Species. 

Plant. 

Bouquet. 

Geranium. 

Monarda. 

Aster. 

Chamaener- 
ium. 

Gilia. 

Bombus  juxtus 

Halictus  pulzenus. .  .  . 
Erynnis  1.  snowi 

Total 

34:107 
1:     2 
1:     1 

2:5 
0:0 
0:0 

6:8 
0:0 
0:0 

23:77 
2:14 
0:  0 

0:0 
0:0 
0:0 

36:110 

2:5 

6:8 

25:91 

0:0 

Expt.  2,  2  hours,  15  minutes,  8h15m  to  10h30m  a.m.,  August  14. 

Bombus  juxtus 

bif  arius 

Total 

Grand  total .  .  . 

24:151 
2:     8 

15i 
0 

7:34 
0 

26  :159 

15i 

7:34 

62:269 

2:5:15i 

6:8 

32:125 

0:0 

Experiments. — In  table  78  the  first  record  is  one  of  natural  competition 
between  fireweed  and  geranium,  the  next  two  are  experiments  in  which 
the  former  was  the  standard  plant  and  the  last  is  an  isolated  one  with 
Frasera,  a  flower  of  similar  form  but  very  different  color. 

Summary. — Chamaenerium  proved  many  times  more  attractive  than 
either  Aconitum  or  Delphinium;  it  received  fewer  visitors  than  Geranium, 
though  this  was  only  exceptionally  true,  and  was  due  to  the  absence  of 
Bombus.  The  usual  efficiency  of  the  columbine  was  lacking  in  competition 
with  Frasera,  in  consequence  of  the  great  attraction  of  the  latter  for  Apis 
and  Bombus. 

PENTSTEMON. 

Comparison. — Of  the  five  species  of  Pentstemon  employed,  P.  glaber, 
glaucus,  and  gracilis  grow  native  in  the  area,  barbatus  and  unilateralis  were 
brought  from  the  foothills,   and  halli  from   the   alpine  meadows.     The 


112 


COMPETITION  AND  CONSTANCY. 


flowers  of  all  are  variously  blue  or  blue-purple  in  color,  with  the  exception 
of  P.  barbatus,  in  which  they  are  vermilion.  The  flowers  of  P.  glaber  are 
the  largest,  decreasing  through  unilateralis,  glaucus,  and  halli  to  gracilis; 
those  of  P.  barbatus  have  a  narrow  tube  as  in  the  last,  but  they  are  much 
longer.  The  secund  clusters  are  most  conspicuous  in  P.  unilateralis  and 
P.  glaber  and  the  open  few- flowered  one  of  P.  barbatus  is  the  least  so,  in  spite 
of  the  brilliant  flowers.     The  pink-purple  corollas  of  Elephantella  groen- 

Table  78. — Natural  and  bouquet  competition  of  Chamaenerium,  and  Frasera. 


Expt.l, half-hour, Hh23m  to  llh53m  a.m.,  July  15. 

Expt.  3, 1  hour,  10h35m  to  llh35m  a.m.,  July  24. 

Species. 

Plant 
Chamae. 

Plant 
G.  caesp. 

Species. 

Plant 
Chamae. 

Bouquet 
Aconitum. 

Apis  mellifica 

Megachile  relativa .  .  . 
texana. . . . 

Osmia  phaceliae 

Prosopis  elliptica 

wootoni 

Protothyreopus  dilec- 

tus 

Sphex  vulgaris 

Atrytone  taxiles 

Total 

0:   0 
4:13 
2:   6 
1:    1 
6:  6 
2:   2 

0:   0 
0:   0 
1:    1 

0:   0 
0:   0 
1:  4 
13:13 
1:   1 

2:   4 
1:    1 
0:   0 

Bombus  appositus .  .  . 

juxtus 

proximus 

Megachile  pugnata. . . 

texana .... 

Vespa  germanica .... 

Atrytone  taxiles 

Total 

42 

140 

7 

4 

10 
2 

47 

0 
4 
0 
0 
0 
0 
0 

252 

4 

16:29 

25:32 

Expt.  4,  1  hour,  QHOF*  to  10h40m  a.m.,  July  14 

Expt.  2,  2}i  hours,  8  to  10  and  10  to  11  a.m., 
August  17. 

Species. 

Plant, 
Frasera. 

Bouquet, 
Aquilegia. 

Species. 

Plant, 
Chamae. 

Bouquet, 
Delphin. 

Apis  mellifica 

Andrena  madronitens 

Bombus  juxtus 

morrisoni.  .  .  . 

73 
3 

30 
1 
0 
0 
0 

1 

2 

101 
4 
49 
1 
0 
0 
0 
1 
2 

0 
1 
1 
0 
1 
1 
1 
0 
0 

0 
2 
1 
0 
3 
3 
1 
0 
0 
n 

Bombus  bifarius 

juxtus 

Prosopis  varif rons .... 

Total 

133 

46 

3 

11 
0 
0 

Osmia  bruneri 

melanotricha  . 
Prosopis  episeopalis  . 

182 

11 

Bombus  Justus 

bifarius 

Monumetha  albifrons 

Total 

121 
16 
4 

1 
0 
0 

Totals 

114:162 

5:10 

141 

1 

landica  are  individually  inconspicuous,  owing  to  the  slender  coiled  tube, 
but  they  are  massed  in  a  compact  cluster  that  has  a  considerable  degree  of 
visibility.  The  amount  of  both  nectar  and  pollen  is  much  less  than  in  the 
various  species  of  Pentstemon.  The  flowers  of  Dodecatheon  meadia  are 
bright  pink  and  of  about  the  size  of  the  smaller  pentstemons;  usually  but 
one  or  two  are  in  bloom  in  a  cluster  at  the  same  time  and  the  amount  of 
nectar  and  pollen  is  small.  The  other  species  concerned  have  been  pre- 
viously described  (plates  7,  8,  and  12). 


PENTSTEMON. 


113 


Experiments. — These  dealt  largely  with  single  and  mixed  bouquets, 
though  both  natural  and  plant-bouquet  competition  were  also  concerned. 


Table  79 

— Bouquet  competition  of  species  of  Pentstemon. 

Separate  bouquets. 

Single  bouquet. 

Expt.  1,  1  hour,  9  to  10  a.m.,  June  19. 

Expt.  4,  2  hours,  9  to  11  a.m.,  July  21. 

Species. 

Glaber. 

Halli. 

Gracilis. 

Species. 

Glab. 

Hall. 

Glauc. 

Eleph. 

Anthophora  simillima. . 

Halictus  pulzenus 

Monumetha  albifrons. . 
Osmia  bruneri 

0 
1 
0 
3 
10 
1 
0 

1 
1 
0 
0 
15 
14 
3 

0 
0 
1 
2 
2 
13 
9 

Bombus  bifarius 

juxtus 

Halictus  (Chloralictus) 

sp 

Osmia  bruneri 

melanotricha .  .  . 
pentstemonis . .  . 

Prosopis  elliptica 

Pseudomasaria  vespoi- 

22 

1 

1 
2 
5 
8 
5 

21 

0 

0 

1 
0 

7 
0 

1 

0 

1 
0 

0 
0 
4 
0 
0 

0 

25 
0 

0 
0 
3i 
0 
Hi 

0 

phaceliae 

Prosopis  basalis 

Total 

15 

34 

:7 

Expt.  2,  1  hour,  10  to  11  a.m.,  June  19. 

Total 

65 

9 

5 

25:14i 

Species. 

Glaber. 

Unilat- 
eral. 

Bar- 

batus. 

Expt.  5,  1  hour,  9  to  10  a.m.,  July  14. 

Anthophora  simillima. . 

Bombus  juxtus 

Halictus  pulzenus 

Monumetha  albifrons. . 

Osmia  phaceliae 

Vespa  germanica 

Atrytone  taxiles 

Total 

1 
4 
2 
1 
2 
1 
2 

0 
2 
0 
0 
0 
0 
0 

0 
0 
0 
0 
0 
0 
0 

Species. 

Pent, 
glab. 

Geran. 
caesp. 

Dodoc. 
meadia 

Anthophora  simillima .  . 

2 
1 

0 

1 
5 

1 

0 
19 

1 
0 
0 
0 

0 
0 

0 
0 
0 
0 

Halictus  (Chloralictus) 

13 

2 

0 

pentstemonis. . . . 
Prosopis  varifrons 

Total 

Expt.  3,  1  hour,  11  a.m.  to  12  m.,  June  19. 

Bombus  juxtus 

Halictus  pulzenus 

Osmia  phaceliae 

Prosopis  varifrons 

Vespa  germanica 

Total 

6 
0 
3 
1 
1 

10 
3 
3 
0 

1 

0 
0 
0 
0 
0 

10 

20 

0 

11 

17 

0 

There  were  no  visitors  to  the  P.  secundiflorus  flowers  when  that  bouquet 
was  placed  6  inches  from  the  P.  gracilis  plants.  However,  when  these 
flowers  were  mixed  in  the  same  cluster,  Osmia  went  from  P.  gracilis  to  P. 
secundiflorus  and  behaved  in  the  same  way  at  both  species.  It  probably 
visited  P.  secundiflorus  in  this  case  without  noticing  that  it  had  gone  to  a 
different  flower.  Although  the  corolla  mouth  of  the  P.  secundiflorus  flower 
is  very  large,  Halictus  went  into  it  upside  down  just  as  in  P.  gracilis. 

Summary. — In  the  competition  with  separate  boquets,  Pentstemon 
halli  and  gracilis  were  about  twice  as  attractive  as  glaber,  owing  to  the  pref- 
erence shown  by  Osmia  and  Prosopis.  P.  barbatus  again  received  no  visits, 
while  the  ratio  between  P.  glaber  and  P.  unilateralis  was  24 :  19,  this  similarity 
being  suggested  by  the  resemblance  of  the  flowers.     The  extra-regional 


114 


COMPETITION  AND  CONSTANCY. 


species,  P.  halli  and  P.  unilateralis,  fared  as  well  or  better  than  the  others, 
the  neglect  of  the  third,  P.  barbatus,  obviously  being  due  to  its  color  or 
shape.  When  combined  in  one  bouquet,  P.  glaber  was  several  times  more 
attractive  than  both  P.  halli  and  P.  glaucus  and  about  twice  as  attractive 
as  Elephantella.  While  Osmia  and  Prosopis  were  both  attracted  by  the 
latter,  the  one  merely  hovered  and  the  other  was  unable  to  probe  the 

Table  80. — Natural  and  bouquet  competition  of  Pentstemon  gracilis. 


Expt.  1,  8  to  10h50m  a.m.,  July  1. 

Expt  3,  9  to  10  a.m.,  June  17. 

Species. 

Plant,  P. 
gracilis. 

Plant,  G. 

caespito- 
sum. 

Species. 

Plant,  P. 
gracilis. 

Bouquet,  R. 
deliciosus. 

Bombus  juxtus 

1 

7 
0 
16 
9 
5 
0 
0 

0 
4 

1 
1 
0 
0 

1 

1 

Halictus  pulzenus 

Osmia  pentstemonis 

Prosopis  varifrons 

Syrphus  americanus 

Total 

5 

1 
1 
2 

0 
0 
0 
0 

Halictus  pulzenus 

Monumetha  albifrons .... 
Osmia  densa 

phaceliae 

Prosopis  basalis 

9 

0 

Pseudomasaris  vespoides. . 

Total 

Expt.  4,  10h35m  to  llh35m  a.m.,  June  17. 

38 

8 

Expt.  2,  8  to  llh20m  a.m.,  July  6. 

Species. 

Bouquet,  P.|    Plant,  R. 
gracilis.      1   deliciosus. 

Apis  mellifica .... 

0 

o 

4 

;                        1 
Colletes  oromontis 0                     24 

Ancistrocerus  sp. .  . 

juxtus j            5 

0 

1 

1 
1 
1 

Total .  . 

0 

25 

Monumetha  albifrons .... 
Osmia  densa.  . 

4 
0 
0 
0 

Expt.  5,  2  to  3  p.m.,  July  12. 

SP 

Muscidae 

Total 

Species. 

Plant,  P. 
gracilis. 

Vials,  C. 
angustif. 

16 

16 

1 
10 

8 

7 

0 
0 
0 
1 

Osmia  melanotricha 

Prosopis  elliptica 

Total 

26 

1 

tightly  coiled  beak.  Though  P.  glaber  attracted  more  species  than  gera- 
nium, the  preference  of  Apis  for  the  latter  gave  it  the  lead.  In  the  natural 
competition  of  Pentstemon  gracilis  and  Geranium  caespitosum  the  ratios 
were  38:8  and  16:16  on  days  about  a  week  apart.  This  was  due  chiefly 
to  the  practical  dropping  out  of  Osmia  and  Prosopis  in  the  second  case.  The 
results  with  bouquets  and  vials  followed  the  rule,  neither  Pentstemon  nor 
Rubus  being  visited  when  it  was  the  bouquet  and  Chamaenerium  flowers  in 


MONARDA   FISTULOSA. 


115 


vials  receiving  but  1  visit  to  26  for  those  of  P.  gracilis  in  the  natural  position. 
The  latter  as  the  standard  was  about  twice  as  attractive  as  P.  secundi- 
florus,  P.  barbatus,  and  Scrophularia  in  a  mixed  bouquet. 

Table  81. — Competition  of  Pentstemon  gracilis  standard  and  a  mixed  bouquet. 


Expt.  1,  1  hour,  11  a.m.  to  12  m.,  July  3. 

Species. 

Plant, 
P.  gracilis. 

Bouquet, 

P.  secund- 

iflorus. 

Bouquet, 
P.  barbatus. 

Bouquet, 
S.  nodosa. 

0:   0 
0:   0 
6:25 
6:45 
1:  4 
2:   3 

1:  3 

3:  9 
0:   0 
2:  4 

1:   3 

0:0 
0:0 
0:0 
0:0 
0:0 
0:0 

0:   0 
0:   0 
0:   0 
0:   0 
1:   4 
3:18 

Total 

15:77 

8:20 

0:0 

4:23 

Expt.  2,  1  hour,  lO^O™  to  ll^O™  a.m.,  June  22. 

0:   0 
1:    1 
8:   8 
1:   1 

1:    1 
1:    1 
1:    1 
1:    1 

0:0 
0:0 
0:0 
0:0 

0:   0 
0:   0 
0:   0 
1:    1 

Syrphus  opinator 

Total 

10:10 

4:   4 

0:0 

1:    1 

25:87 

12:24 

0:0 

5:23 

MONARDA  FISTULOSA. 

Comparison. — A  large  number  of  species  were  used  in  competition 
with  Monarda,  in  natural,  bouquet,  and  group  installations.  The  only  one 
to  resemble  it  at  all  closely  was  Gilia  aggregata,  with  long,  tubular  pink 
corollas  in  an  elongated  cluster.  The  gamopetalous  flowers  of  Gentiana 
parryi  and  Campanula  rotundifolia  departed  widely  in  shape,  color,  and 
arrangement,  as  did  also  the  zygomorphic  Delphinium  and  the  actino- 
morphic  Geranium,  Chamaenerium,  and  Calochortus  gunnisoni.  This  was 
essentially  true  also  of  the  three  composites  Achillea  millefolium,  Aster 
bigelovi,  and  Erigeron  macranthus,  the  first  with  white  rays  and  the  last 
two  with  purple  ones  (plates  6,  7,  8,  and  10). 

Experiments. — These  include  natural  and  bouquet  competition,  and 
the  competition  results  of  the  Monarda  calendars  given  in  the  preceding 
chapter. 

Summary. — In  natural  competition  with  Geranium  caespitosum,  Cam- 
panula rotundifolia,  and  Achillea  millefolium,  Monarda  was  slightly  less 
attractive  than  Geranium,  owing  to  the  decided  preference  of  Bombus  and 
Halictus  for  the  latter.  When  Monarda  was  the  standard  in  competition 
with  a  bouquet  of  Gentiana,  Erigeron,  and  Calochortus,  it  was  about  twice 


116 


COMPETITION  AND  CONSTANCY. 

Table  82. — Natural  and  bouquet  competition. 


Expt.  1,  \\i  hours,  8  to  9h30m  a.m.,  July  3  . 

Expt.  3,  2  hours,  8h57m  to  10b57m  a.m.,  July  20. 

Species. 

Plant, 
Mon. 

Plant, 
Ger. 

Species. 

Plant, 
Mon. 

Bouquet, 
Chamae. 

Bombus  juxtus 

bifarius 

proxiruus. . .  . 
Colletes  oromontis.  .  . 
Argynnis  atlantis.  .  .  . 
Thanaos  martialis. . .  . 

Total 

17:44 

0 

0 

0 

1:    1 

1:    1 

74 
85 
5 
2 
0 
0 

Anthophora  smithi. .  . 

Bombus  juxtus 

appositus.  .  . 

Megachile  pugnata. . . 

texana. . . . 

Vespa  germanica.  .  . . 

Dejeania  vexatrix. . .  . 

0 
12:169 

0 

0 

0 
1:   3 

0 

0 
1:   3 

1:   2 
35:222 
3:   8 
2:   4 
1:   2 

0 
1:   9 
3:   4 

0 

19:46 

166 

Argynnis  atlantis. .  .  . 
Total 

Expt.  2,  1  hour,  11  a.m.  to  12  m.,  August  17. 

14:175 

46:251 

Species. 

Plant, 
Mon. 

Bouquet, 
Delph. 

Bombus  proximus. . . . 
morrisoni. .  .  . 
edwardsi .... 

juxtus 

bifarius ..... 

Total 

134 
19 
46 
14 
11 

0 
96 
17 
6 
0 

224 

119 

Table  83. — Natural  competition  of  a  group. 


One  and  one-half  hours,  9  to  10h30m  a.m.,  August  2. 

Species. 

Monarda. 

Geranium. 

Campanula. 

Achillea. 

0 
4 
0 

30 
0 
0 
0 
2 
0 
0 
0 
4 

33 

50 
0 
9 
1 
13 
10 
2 
0 
2 
1 
0 
0 
0 

0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 

0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
3 
0 
0 

Halictus  (Lasioglossum)  sp 

Total 

73 

88 

0 

3 

as  attractive.  In  a  test  of  plants  of  Monarda  and  Geranium,  the  latter  was 
more  than  three  times  as  attractive,  Bombus  bifarius  going  to  it  alone,  and 
B.  juxtus  giving  it  a  marked  preference.  Similar  behavior  of  B.  bifarius 
was  the  chief  factor  in  causing  a  bouquet  of  Chamaenerium  to  be  preferred 


MONARDA   FISTULOSA. 


117 


to  a  plant  of  Monarda.  However,  while  the  latter  obtained  only  a  third  as 
many  visitors,  these  averaged  12  visits  to  it  in  contrast  to  6  for  the  former. 
In  the  three  related  series,  the  total  number  of  visits  to  normal  Monarda 
flowers  was  2,397,  to  mutilated  ones  452,  and  to  the  various  competing 
flowers  449.     There  were  outstanding  differences  between  the  different 

Table  84. — Bouquet  competition  of  a  group. 


Two  and  a  half  hours,  9  to  llh30m,  August  5. 

Species. 

Plant, 
Monarda. 

Bouquet, 
Gentiana. 

Bouquet, 
Erigeron. 

Bouquet, 
Calochortus. 

0 
26 
24 

0 

1 
0 
1 
2 
16 
0 

0 
0 
0 
0 
0 
0 
0 
0 
0 
0 

3 
0 
0 
9 
1 
0 
2 
0 
2 
11 

0 
0 
0 
9 
2 
1 
0 
0 
0 
0 

Pseudomasaris  vespoides 

Total 

70 

0 

28 

12 

Table  85. — Competition  of  normal  and  mutilated  Monarda  and  other  species. 
First  Series. 


Species. 


Normal 
Monarda. 


Total 
mutilated 
Monarda. 


Monarda 
composite. 


Chamae- 
nerium 


Normal 
Geranium. 


Total 
competi- 
tors. 


Clisodon 

Bombus  appositus.  . 

bifarius. . .  . 

occidentalis 

Argynnis 

Atrytone 

Erynnis 

Prosopis 

Total 

Clisodon 

Bombus  appositus .  . 

bifarius .... 

occidentalis 

Monumetha 

Syrphus 

Atrytone 

Gnophaela 

Total 

Grand  total . . 


87 


0 
0 
0 
0 
0 
5b:3 
0 
0 


5b: 


0 
0 
0 
0 
0 
0 
bwr 
0 


bwr 


b:4  w:r 


12 


13 


34 


118 


COMPETITION  AND  CONSTANCY. 


Table  85- — Competition  of  normal  and  mutilated  Monarda  and  other  species — Continued. 

Second  Series. 


Species. 

Normal 
Monarda. 

Total 
muti- 
lated. 

Gilia 
heads. 

Chamae. 
head. 

Total 
heads. 

Norm. 
Chamae. 

Norm. 
Ger. 

Total 
competi- 
tors. 

621 

220 

94 

13 

13 

100 

15 
28 
45 
0 
0 
43 

0 
6  Mon. 

0 

0 

0 
1  Mon. 
14  p. 

0 
0 
0 
0 
0 
0 

0 
6  Mon. 

0 

0 

0 
1  Mon. 

0 
8 
1 
0 
6 
26 

0 
0 
0 
0 
0 
10 

1 

8 

0 

6 

50 

Bom  bus  appositus .  .  . 

juxtus 

morrisoni .  .  . 

Total 

1,061 

131 

7  Mon. 

0 

7  Mon. 

41 

10 

66 

9 

27 

13 

1 

40 

0 

0 

0 

4 

3 
0 
0 
0 
3 
0 
0 
0 
0 
0 

0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 

0 
0 
1 
0 
0 
0 
0 
0 
0 
0 
2  Mon. 

0 
0 

0 
0 
0 
0 
0 
0 
0 
2  Mon. 

0 
0 
3 
0 
10 
0 
0 
0 
0 
0 
0 

0 

0 
22 
0 
0 
14 
1 
2 
1 
1 
0 

0 

0 

26 

0 

10 

14 

1 

2 

0 

Bombus  appositus.  .  . 

juxtus 

edwardsi. . . . 

hunti 

occidentalis . 

morrisoni.  .  . 
H.  (Lasioglossum)  sp. 

P.  varifrons 

Erynnis 

s 

Total 

94 

7 

0 

1:2  Mon. 

1:2  Mon. 

13 

41 

55 

Grand  total. . . 

1,155 

138 

7  Mon.  Jl:2Mon. 

1:9  Mon. 

54 

51 

121 

Third  Series. 


Species. 

Nor- 
mal. 

Total 
muti- 
lated. 

Gilia 
head. 

Chamae. 
head. 

Total 
heads. 

Norm. 
Chamae. 

Norm. 
Ger. 

Norm. 
Aster. 

Total 
competi- 
tors. 

309 
151 
113 
2 
161 
187 

51 

7 
37 

1 
77 
35 

0 
0 
0 
3 
3 
0 

0 
0 
2 
4 
0 
0 

0 
0 
2 
7 
3 
0 

7 
1 
25 
0 
7 
1 

0 
0 

2 
0 
1 
0 

0 
0 
0 
0 
0 

8 

1 
29 

7 
11 

1 

Bombus  appositus. .  .  . 

juxtus 

morrisoni. . .  . 

Total 

923 

208 

6 

6 

12 

41 

3 

1 

57 

38           27 

0 
0 
0 
0 
0 
0 
0 
0 
1 
0 
0 
0 
0 
0 

0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 

0 
0 
0 
0 
0 
0 
0 
0 
1 
0 
0 
0 
0 
0 

0 

9 

2 

25 

90 

0 

9 

0 

24 

0 

2 

0 

0 

1 

0 
0 
0 
1 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 

0 
0 
0 
0 
1 

51 
7 
2 

12 
0 
0 
0 
0 
0 

0 

9 

2 

26 

91 

51 

16 

2 

37 

0 

2 

0 

0 

1 

Bombus  juxtus 

morrisoni. . .  . 

bifarius 

hunti 

0 

16 

8 

0 

2 

0 

0 

125 

21 

4 

17 

1 

0 

0 
0 
0 
0 
0 
0 
0 
41 
8 
0 
0 
0 
0 

Total 

232 

76 

1 

0 

1 

162 

1 

73 

237 

Grand  total .  .  . 

1,155 

284 

7 

6 

13 

203 

4 

74 

294 

POLLEN    LOADS. 


119 


series  as  well  as  between  the  two  calendars  made  at  the  same  time,  as  shown 
in  table  86. 

The  greatest  difference  is  shown  by  the  two  calendars  of  series  3,  in  which 
the  marked  constancy  of  Clisodon  and  Bombus  appositus  and  their  vastly 
greater  abundance  in  the  one  place  furnishes  the  explanation.  Corre- 
sponding differences  may  also  be  noted  with  respect  to  the  response  to  the 
several  competitors.  Normal  Geranium  flowers  and  composite  heads  of 
Chamaenerium  were  twice  visited  equally,  though  as  a  rule  these  artificial 
heads  were  neglected.  A  marked  exception  occurred  in  the  second  series, 
where  14  flowers  of  a  pure  Gilia  head  were  visited  by  Argynnis.  As  between 
normal  Chamaenerium  and  normal  Geranium,  the  former  was  thrice  as 
attractive  all  told,  though  the  relative  positions  were  reversed  in  the  cal- 
endars of  the  second  series.  In  this  competition  B.  bifarius  and  B.  hunti 
were  partial  to  Chamaenerium  and  B.  occidentalis  to  Geranium,  while  B. 
juxtus  preferred  Geranium  in  one  series  and  Chamaenerium  in  the  other. 


Table  86. — Summary  of  normal  and  competing  flowers  by  series  and  calendars. 


Series  1. 

Series  2. 

Series  3. 

Nor- 
mal. 

Com- 
peting. 

Ratio. 

Nor- 
mal. 

Com- 
peting. 

Ratio. 

Nor- 
mal. 

Com- 
peting. 

Ratio. 

50 
37 

25 
9 

2:1 
4:1 

1,061 

94 

66 
55 

16:1 
2:1 

923 
232 

57 

237 

16:1 

Total 

87 

34 

3:1      lis* 

121          Q-i 

1,155 

294 

1:4 

COMPOSITION  AND  WEIGHT  OF  POLLEN  LOADS. 

Value  and  methods. — While  occasional  observations  of  the  purity  of 
pollen  loads  have  been  recorded  (Bennett,  1874;  Perez,  1903),  no  previous 
microscopical  analysis  of  loads  seems  to  have  been  made.  The  latter  were 
undertaken  in  the  first  place  as  a  check  upon  the  habits  observed  in  the 
field,  and  were  extended  to  include  the  weight  of  the  bee  and  its  pollen  load 
as  a  measure  of  its  efficiency  in  collecting  and  in  flight.  Unfortunately,  it 
was  not  until  these  preliminary  studies  were  practically  finished  that  it  was 
realized  that  the  time  of  flight  should  have  been  recorded,  since  the  degree 
of  constancy  varies  much  between  morning  or  evening  on  the  one  hand 
and  mid-day  on  the  other.  There  is  also  an  evident  difference  in  indi- 
vidual efficiency,  which  can  be  determined  only  by  the  use  of  marked  bees. 

As  a  rule  the  bees  were  weighed  immediately  after  being  caught,  the 
load  completely  removed  by  means  of  a  needle,  and  the  body  weighed 
again.  In  a  few  cases  the  bees  were  dry,  and  corresponding  allowance  must 
be  made  with  respect  to  the  percentage  weight  of  the  load.  In  the  tables 
the  name  of  the  species  on  which  the  insect  was  captured  is  given  first  in 
each  case;  when  the  bee  had  collected  none  of  this  pollen,  it  is  indicated. 
For  a  number  of  specimens  previously  collected  (designated  by  a  letter), 
the  pollen  was  examined,  but  the  weight  of  the  load  was  not  determined. 


120 


COMPETITION  AND  CONSTANCY. 


Table  87. 


-Composition  and  weight  of  pollen  loads. 
Apis  mellifica. 


Date. 

Catalogue 
No. 

Weight  of 
bee. 

Weight  of 
load. 

Load,  p.  ct. 
of  bee's 
weight. 

Composition  of  load. 

gm. 

gm. 

p.  ct. 

June  21 

1 

0.0780 

0.0168 

21.4 

Rubus  deliciosus,  pure. 

Do. 

2 

.0800 

.0190 

24.0 

Do. 

Do. 

3 

.0710 

.0188 

26.5 

Do. 

Do. 

4 

.0858 

.0210 

24.5 

Do. 

Do. 

5 

.0930 

.0120 

13.0 

Do. 

Do. 

6 

.0820 

.0190 

23.2 

Do. 

Do. 

7 

.0738 

.0120 

16.2 

Do 

Do. 

8 

.0800 

.0250 

31.2 

Do. 

Do. 

9 

.0725 

.0235 

32.4 

Do. 

Do. 

10 

.0670 

.0200 

30.0 

Do. 

Dry. 

June    7 

49 

.0262 

.0113 

44.0 

Do. 

Do. 

50 

.0315 

.0125 

39.0 

Do. 

Do. 

51 

.0250 

.0095 

38.0 

Do. 

Do. 

52 

.0250 

.0120 

50.0 

Do. 

Do. 

99 

.0250 

.0200 

8.0 

Do. 

Do. 

100 

.0275 

.0145 

52.0 

Do. 

Do. 

101 

.0300 

.0108 

36.0 

Do. 

Do. 

102 

.0275 

.0135 

49.0 

Do. 

Do. 

103 

.0280 

.0145 

52.0 

Do. 

Do. 

104 

.0230 

.0045 

19.0 

Do. 

Do. 

105 

.0260 

.0040 

16.0 

Do. 

Do. 

106 

.0335 

.0065 

19.0 

Do. 

July  23 

123 

.0750 

.0085 

11.0 

Geranium  caespitosum,  pure. 

Do. 

125 

.1020 

.0090 

9.0 

Geranium  caespitosum,  1  p.  ct. 
Holodiscus  dumosus,  99  p.  ct. 

July  28 

167 

.0760 

.0190 

25.0 

Chamaenerium    angustifolium, 
pure. 

Do. 

169 

.0900 

.0080 

9.0 

Do. 

July  30 

170 

.1015 

.0185 

18.0 

Do. 

Do. 

171 

.0950 

.0245 

26.0 

Do. 

Do. 

172 

.0950 
Number 
examined. 

.0130 

14.0 

Do. 

A 

1 

Geranium  caespitosum,  99  p.  ct. 

R.  acic.  and  P.  gracilis,  1  p.  ct. 

B 

1 

Solidago,  95  p.  ct.;  ?5. 

C 

1 

Petalostemon  purpureus,  99  p.  ct. 

Andrena 

2RATAEGI. 

gm. 

gm. 

p.  ct. 

June  22 

30 

0 . 0469 

0 . 0058 

12 

Rubus  deliciosus,  99.5  p.  ct. ;  ?.5. 

Do. 

31 

.0537 

.0053 

10 

Rubus  deliciosus,  pure. 

Do. 

40 

.0520 

.0075 

14 

Do. 

Do. 

41 

.0687 

.0095 

14 

Do. 

July    3 

68 

.0520 

.0090 

17 

Rosa  acicularis,  pure. 

July     6 

78 

.0490 

.0070 

5 

Rubus  deliciosus,  pure. 
(Rubus  deliciosus,  25  p.  ct. 
\  Rubus  strigosus,  75  p.  ct. 

Do. 

79 

.0470 

.0055 

11 

Do. 

80 

.0500 

.0050 

10 

Rubus  strigosus,  pure. 

July  23 

128 

.0395 

Number 
examined. 

.0035 

8 

Geranium  caespitosum,  10  p.  ct. 
Holodiscus  dumosus,  90  p.  ct. 

A 
B 

2 

7 

Prunus  demissa,  pure. 
Rubus  strigosus,  pure. 

1 

POLLEN   LOADS. 

Table  87. — Composition  and  weight  of  pollen  loads — Continued. 
Andrena  edwineae. 


121 


Date. 

Catalogue 
No. 

Weight  of 
bee. 

Weight  of 
load. 

Load,  p.  ct. 
of  bee's 
weight. 

Composition  of  load. 

C 

gm. 

1 

gm. 

p.  ct. 

Jamesia  americana,  pure. 

Andrena  madronitens. 

July  23 

July  24 
July  25 

127 

135 

148 

D 

gm. 
0.0320 

.0365 

.0380 

2 

gm. 
0.0045 

.0050 
.0080 

p.  ct. 
14 

14 
21 

Geranium  caespitosum,   1  p.  ct. 
Holodiscus  dumosus,  97  p.  ct. 
Oenothera  biennis,  2  p.  ct. 
Frasera  speciosa,  97  p.  ct. 
Geranium  caespitosum,  3  p.  ct. 
Frasera  speciosa,  5  p.  ct. 
Sedum  stenopetalum,  95  p.  ct. 
Rubus  deliciosus,  pure. 

Andrena  vicina. 

June  23 
Do. 

28 
29 

E 

F 

gm. 

0.1045 

.0700 

Number 

examined. 

2 

1 

gm. 

0.0065 

.0100 

p.  ct. 
6 
13 

Rubus  deliciosus,  pure. 
Do. 

Rosa  acicularis,  99  p.  ct. ;  ?1. 
Rubus  deliciosus,  99  p.  ct. ;  ?1. 

ANTHOPHORA    SIMILLIMA. 

June  23 

July    3 
July    8 

32 

62 
94 

A 
B 

gm. 
0.1555 

.1275 

.1400 
-  Number 
examined. 

1 
1 

gm. 
0.0079 

.0095 
.0110 

p.  ct. 
5.0 

8.0 
8.0 

[Rosa  acicularis,  90  p.  ct. 

1  Dodocatheon  meadia,  8  p.  ct. 

(Pentstemon  gracilis,  2  p.  ct. 

28  conifer  grains. 
(Rosa  acicularis,  99  p.  ct. 
\Pentstemon  gracilis,  1  p.  ct. 

Rosa  acicularis,  pure. 

(Lithospermum  canescens,  98  p.ct. 
\  Rosa  acicularis,  1  p.  ct.,  ?1  p.  ct. 
fCapnoides  aureum,  98  p.  ct. 
\Aragalus  lamberti,  2  p.  ct. 

»                                                                                                      BOMBUS     APPOSITUS. 



A 

Number 
examined. 

1 

p.  ct. 

Petalostemon  purpureus,  70  p.  ct. 
Compositae,  30  p.  ct. 

122  COMPETITION  AND  CONSTANCY. 

Table  87. — Composition  and  weight  of  -pollen  loads — Continued. 

BOMBU8    BIFARIUS. 


Date. 

Catalogue 
No. 

Weight  of 
bee. 

Weight  of 
load. 

Load,  p.  ct. 
of  bee's 
weight. 

Composition  of  load. 

No. 

gm. 

p.  ct. 

B 

1 

Pentstemon  glaber,  pure. 

c 

2 

(Geranium  caespitosum,  2  p.  ct. 
\  Pentstemon  gracilis,  98  p.  ct. 

D 

1 

Pentstemon  gracilis,  pure. 

E 

1 

fPentstemon  gracilis,  99  p.  ct. 
1  Geranium  sp.,  0.1;  ?.9  p.  ct. 

[Pentstemon  gracilis,  90  p.  ct. 

F 

1 

\  Rosa  acicularis,  5  p.  ct. 
iGeranium  caespitosum,  5. 

G 

. 

(Pentstemon  gracilis,  99  p.  ct. 

\Rosa  acicularis,  1  p.  ct. 

gm. 

July  22 

120 

0.0800 

0.0220 

27.0 

Jamesia  americana,  pure. 

July  23 

124 

.0780 

.0060 

7.0 

(Geranium  caespitosum,  none. 
\  Holodiscus  dumosus,  pure. 

Do. 

126 

.0640 

.0295 

46.0 

fGeranium  caespitosum,  1  p.  ct. 
\Holodiscus  dumosus,  99  p.  ct. 

July  24 

136 

.0825 

.0065 

7.0 

Frasera  speciosa,  pure. 

July  26 

137 

.0875 

.0050 

5.0 

Campanula  rotundifolia,  pure. 

Do. 

145 

.0755 

.0140 

11.0 

Sedum  stenopetalum,  pure. 
Chamaenerium  angustifolium,  1 

July  31 

173 

.0670 

.0090 

13.0 

p.  ct. 

Holodiscus  dumosus,  99  p.  ct. 

BOMBUS 

JUXTUS. 

gm. 

gm. 

p.  ct. 

June  23 

33 

0.1124 

0.0231 

20.0 

Rubus  deliciosus,  pure. 

Do. 

34 

.0295 

.0045 

19.0 

fRubus  deliciosus,  30  p.  ct. 
\ Pentstemon  gracilis,  70  p.  ct. 

Do. 

35 

.0427 

.0021 

5.0 

fRubus  deliciosus,  99  p.  ct. 
\Rosa  acicularis,  1  p.  ct. 

Do. 

36 

.0228 

.0022 

10.0 

Rubus  deliciosus,  pure. 

Do. 

37 

.0225 

.0025 

11.0 

Do. 

Do. 

38 

.0090 

.0021 

24.0 

Do. 

Do. 

39 

.0075 

.0018 

24.0 

Do. 

Do. 

45 

.0860 

.0025 

26.0 

Do. 
4  conifer  grains. 

July    3 

61 

.0870 

.0255 

29.0 

fRosa  acicularis,  pure. 
\    conifer  grain. 

Do. 

71 

.0820 

.0130 

16.0 

fRosa  acicularis,  pure. 
\  4  conifer  grains. 
[Rosa  acicularis,  none. 

Do. 

72 

.1150 

.0200 

17.0 

j  Rubus  deliciosus,  50  p.  ct. 
|  Rubus  strigosus,  50  p.  ct. 
1 2  conifer  grains. 

July    6 

73 

.0725 

.0315 

43 

fRubus  deliciosus,  pure. 
|6  conifer  grains. 

Do. 

74 

.0700 

.0210 

30.0 

fRubus  deliciosus,  pure 
1 2  conifer  grains. 

Do. 

75 

.0940 

.0365 

39.0 

fRubus  deliciosus,  pure. 
\3  conifer  grains. 

June    5 

110 

.0900 

.0555 

61.0 

Rubus  deliciosus,  pure. 

Do... 

111 

.1000 

.0390 

39.0 

Do. 

Do. 

112 

.1370 

.0130 

9.0 

Do. 

July  17 

113 

.1000 

.0150 

15.0 

Rosa  acicularis.  pure, 

POLLEN   LOADS. 


123 


Table  87.- 


-Composition  and  weight  of  pollen  loads — Continued. 
Bombus  juxtus — Continued. 


Date. 

Catalogue 
No. 

Weight  of 
bee. 

Weight  of 
load. 

Load,  p.  ct. 
of  bee's 
weight. 

Composition  of  load. 

firm. 

gm. 

p.  ct. 

July  17 

114 

0 . 0850 

0 . 0050 

3.0 

Rosa  acicularis,  pure. 
fHolodiscus  dumosus,  70  p.  ct. 

July  21 

116 

.0915 

0.0110 

12.0 

\  Rosa  acicularis,  29  p.  ct. 
(Oenothera  biennis,  1  p.  ct. 

July  22 

117 

.0880 

.0125 

1.0 

fPotentilla  sp.,  85  p.  ct.,  ?10  p.  ct. 
\  Chamaenerium  angustifolium,  5 
p.  ct. 
Campanula  rotundifolia,  pure. 

July  26 

138 

.1010 

.0045 

4.0 

July  25 

147 
1 

.0955 

.0135 

14.0 

fCarduus  hookerianus,  pure. 

\  1  conifer  grain. 

f  Aconitum  columbianum,  99  p.ct. 

\Chamaenerium  angustifolium,  1 

p.  ct. 
fPentstemon  gracilis,  99  p.  ct. 
\Rosa  acicularis,  1  p.  ct. 

m 

n 

Astragalus   drummondi,   pure. 
fPentstemon  gracilis,  99  p.  ct. 
[Geranium  caespitosum,  1  p.  ct. 

0 

Bombus  ] 

CIRBVELLUS. 

July    3 

70 

0.5940 

0.0275 

4 

Frasera  speciosa,  pure. 

July  25 

149 

.2395 

.0065 

12 

Castilleia  p.  occidentalis  pure. 

Do. 

150 

.1000 

.0200 

20 

Do. 

Do. 

151 

.1470 

.0190 

13 

Do. 

Do. 

152 

.1030 

.0100 

9 

Do. 

Do. 

153 

.0720 

.0140 

20 

Do. 

Do. 

154 

.0700 

.0100 

13 

Do. 

Do. 

155 

.1480 

.0140 

9 

Do. 

Do. 

156 

.2700 

.0380 

14 

fPedicularis  parryi,  none. 
\Castilleia  p.  occidentalis,  pure. 

Do. 

157 

.0600 

.0050 

8 

Castilleia  p.  occidentalis,  pure. 

Do. 

158 

.1020 

.0315 

30 

fPentstemon  glaber,  95  p.  ct. 
\Potentilla  pulcherrima,  5  p.  ct. 

Do. 

159 

.1045 

.0095 

9 

Castilleia  p.  occidentalis,  pure. 

Do. 

160 

.0800 

.0220 

20 

Do. 

Do. 

161 

.1200 

.0090 

8 

f  Castilleia  p.  occidentalis,  90  p.  ct. 
\Potentilla  sp.,  10  p.  ct. 

Do. 

162 

.1450 

.0250 

17 

Castilleia  p.  occidentalis,  pure. 
fTrifolium  dasyphyllum,  50  p.  ct. 

Do. 

163 

.1800 

.0200 

11 

i  Castilleia     p.    occidentalis,    48; 
1      ?2  p.  ct. 

Do. 

164 

.1050 

.0220 

12 

fTrifolium  dasyphyllum,  50  p.  ct. 
\  Castilleia  p.  occidentalis,  50. 

Do. 

165 

.0805 

.0085 

11 

fTrifolium  dasyphyllum,  97  p.  ct. 
\Composite,  3  p.  ct. 

E 

OMBUS    OCC 

DENTALIS. 

June  30 

48 

0.1400 

0.0250 

18.0 

fRosa  acicularis,  99  p.  ct. 
\Geranium  caespitosum,  1  p.  ct. 

July    3 

63 

.1330 

.0530 

40.0 

Rosa  acicularis,  pure. 

Do. 

64 

.1400 

.0390 

28.0 

fRosa  acicularis,  95  p.  ct. 
\Rubus  deliciosus,  5  p.  ct. 

124 


COMPETITION  AND  CONSTANCY. 


Table  87. — Composition  and  weight  of  pollen  loads — Continued. 
Bombus  occidentalis — Continued. 


Date. 

Catalogue 
No. 

Weight  of 
bee. 

Weight  of 
load. 

Load,  p.  ct. 
of  bee's 
weight. 

Composition  of  load. 

gm. 

gm. 

p.  ct. 

July    6 

76 

0.1060 

0.0080 

7.0 

Rubus  deliciosus,  pure. 

July    8 

90 

.1650 

.0420 

25.0 

Rosa  acicularis,  pure. 

June    5 

107 

.1385 

.0650 

47.0 

Rubus  deliciosus,  pure. 

Do. 

108 

.1620 

.0727 

45.0 

Do. 

Do. 

109 

.1590 

.0730 

46.0 

Do. 

July  22 

119 

.2450 

.0625 

25.0 

Jamesia  americana,  pure. 

July  23 

122 

.1750 

.0465 

26.0 

/Geranium  caespitosum,  5  p.  ct. 
\Holodiscus  dumosus,  95  p.  ct. 

July  22 

134 

.1580 

.0300 

19.0 

Mentzelia  multifiora,  pure. 
Chamaenerium  angustifolium,  1 

July  31 

174 

.0955 

.0045 

4.0 

p.  ct. 

Holodiscus  dumosus,  99  p.  ct. 

Aug.    5 

175 
H 

.1435 

.0355 

24.0 

fGeranium  caespitosum,  2  p.  ct. 
(Allium  recurvatum,  98  p.  ct. 
Linaria  vulgaris,  pure. 
/Calochortus  gunnisoni,  95  p.  ct. 
^Geranium  caespitosum,    5  p.  ct. 

I 

J 

(Delphinium  scopulorum,  7  p.  ct. 

jCalochortus  gunnisoni,  93  p.  ct. 

K 

f Delphinium  scopulorum,  35  p.  ct. 

1  Composite,  65  p.  ct. 

Bombus  occidentalis: 
Cat.  No.  L 


?10 


?2 


Percentage 

composition 

of  load. 

(Delphinium  scopulorum 95 

[Composite 5 

M Delphinium  scopulorum 85;    ?15 

N Delphinium  scopulorum 99 ;      ?  1 

O Chamaenerium  angustifolium 98;      ?2 

p                          /Chamaenerium  angustifolium 95 

\Composite 5 

Q Chamaenerium  angustifolium 90 ; 

■p                          /Chamaenerium  angustifolium 95 

\  Composite 5 

o                         j  Chamaenerium  angustifolium 80 

\Composite 20 

T Carduus  hookerianus 98; 

Bombus  centralis: 

^       XT     TT                        /Delphinium  scopulorum 10 

Cat-  No-  U \  Composite 90 

Bombus  edwardsii: 

Cat.  No.  V Petalostemon  purpureus i 99; 

w                       /Petalostemon  purpureus 90 

\Composite 10 

■^                         /Calochortus  gunnisoni 40 

(Composite 60 

Bombus  fervidus: 

Cat.  No.  Y Petalostemon  purpureus 98; 

Bombus  flavifrons: 

p       -IJ     „                          fCalochortus  gunnisoni 45 

\  Composite 45 

Chamaenerium  angustifolium 10 

Bombus  hunti: 

Cat.  No.  a Chamaenerium  angustifolium 75; 

Bombus  kirbyellus: 

Cat.  No.  b Rubus  deliciosus 99; 


POLLEN   LOADS. 


125 


Table  87. — Composition  and  weight  of  pollen  loads — Continued. 


Percentage 
composition 
of  load. 


fChamaenerium  angustifolium 1 

[Rosa  acicularis 99 


Bombus  morrisoni : 
Cat.  No.  c 

Bombus  proximus: 

p,  .    xt      j                          (Rosa  acicularis 99 

Uat.  No.  d \Chamaenerium  angustifolium 1 

e Rosa  acicularis pure 

f Rubus  strigosus pure 

J  Rosa  acicularis 99 

g [Rubus  strigosus 1 

Bombus  rufocinctus: 

pi  f  XT     i,                         /Solidago  missouriensis 10 

•   \Petalostemon  purpureus 90 

Chamaenerium  angustifolium 50 

Petalostemon  purpureus 50 

Calochortus  gunnisoni 90 

j -j  Geranium  caespitosum 2 

Composite 2 ; 

( Solidago  missouriensis 10 

' '   Petalostemon  purpureus 90 


Clisodon  terminates 


Date. 

Catalogue 
No. 

Weight  of 
bee. 

Weight  of 
load. 

Load,  p.  ct. 
of  bee's 
weight. 

Composition  of  load. 

July  17 

115 

gm. 
0.1010 

gm. 
0.0040 

p.  ct. 
4.0 

(Rosa  acicularis,  70  p.  ct. 
i  Mertensia  sibirica,  29  p.  ct. 
[Geranium  caespitosum,  1  p.  ct. 

COLLETES    OROMONTIS. 

July  23 

133 

gm. 
0.0045 

gm. 
0.0015 

p.  ct. 
33.0 

fGeranium  caespitosum,  1  p.  ct. 
\Holodiscus  dumosus,  99  p.  ct. 

HaLICTUS    MEDIONITEN9. 

June  23 

July    8 
July    8 
July  23 

46 

96 
97 
130 

gm. 
0.0011 

.0320 
.0058 
.0060 

gm. 
0 . 0003 

.0030 

.0012 
.0020 

p.  ct. 
27.0 

9.0 
21.0 
33.0 

Rubus  deliciosus,  70  p.  ct. 
■  Rosa  acicularis,  25  p.  ct. 

Potentilla  pulcherrima,  5  p.  ct. 
J  Rosa  acicularis,  95  p.  ct. 
\Rubus  deliciosus,  5  p.  ct. 

Rosa  acicularis,  pure. 
/Geranium  caespitosum,  none. 
\Holodiscus  dumosus,  pure. 

Halicttjs  pulzenus. 

A 

B 
C 
D 

fGeranium  caespitosum,  none. 
\Unknown,  pure. 

Geranium  richardsoni,  pure. 

Rosa  acicularis,  pure. 

Rubus  strigosus,  pure. 

126 


COMPETITION  AND  CONSTANCY. 


Table  87. — Composition  and  weight  of  pollen  loads — Continued. 
Megachile  pugnata. 


Date. 

Catalogue 
No. 

Weight  of 
bee. 

Weight  of 
load. 

Load,  p.  ct. 
of  bee's 
weight. 

Composition  of  load. 

gm. 

p.  ct. 

Petalostemon  purpureus,  13  p.  ct. 

A 

Geranium  caespitosum,  2  p.  ct. 

B 

Carduus  hookerianus,  pure. 

Megachile  wootoni  calogasteb. 

gm. 

gm. 

p.  ct. 

June  29 

47 

0.0900 

0.0048 

5.3 

fRosa  acicularis,  95  p.  ct. 
1  Rubus  deliciosus,  1,  ?4  p.  ct. 

July    3 

65 

.1110 

.0075 

7.0 

JRosa  acicularis,  99  p.  ct. 
\  Rubus  deliciosus,  1  p.  ct. 

Do. 

66 

.0980 

.0095 

10.0 

Rosa  acicularis,  pure. 

July    8 

91 
C 

D 

.0995 

.0080 

8.0 

Do. 

Do. 
fPentstemon  glaber,  99  p.  ct. 
\  Rosa  acicularis,  1  p.  ct. 

[Rosa  acicularis,  99  p.  ct. 

E 

4  Chamaenerium  angustifolium,  1 

[     p.  ct. 

F 

Rubus  deliciosus,  pure. 

Megachile  texana. 

gm. 

gm. 

p.  ct. 

[Chamaenerium  angustifolium,  80 

G 

J      p.  ct. 

iRosa   acicularis,    10   p.    ct.,  ?10 

[     p.  ct. 

June  22 

24 

0.1160 

0.0125 

11.0 

Rubus  deliciosus,  pure. 

Megachile  sp. 

gm. 

gm. 

p.  ct. 

July    3 

67 

0.0915 

0.0035 

3.0 

Rosa  acicularis,  pure. 

July  26 

139 

.1090 

.0045 

4.0 

Campanula  rotundifolia,  pure. 

Do. 

140 

.0850 

.0190 

22.0 

Campanula  rotundifolia,  50  p.ct. 
?50  p.  ct. 

Do. 

141 

.0820 

.0085 

10.0 

Campanula  rotundifolia,  pure. 
[Campanula  rotundifolia,  50  p.ct. 

Do. 

142 

.1125 

.0135 

12.0 

\  Chamaenerium  angustifolium,  49 

[     p.  ct.,  ?1  p.  ct. 

[Campanula  rotundifolia,  33  p.ct. 

Do. 

143 

.1185 

.0105 

9.0 

\  Chamaenerium  angustifolium,  33 
(     p.  ct.,  ?34  p.  ct. 

July  28 

168 

.0585 

.0030 

5.0 

Chamaenerium    angustifolium, 

pure. 
[Geranium  caespitosum,  5  p.  ct. 

Aug.    5 

177 

.0940 

.0060 

6.0 

\  Erigeron  macranthus,  90  p.  ct. 
[Oenothera  biennis,  5  p.  ct. 

Do. 

178 

.1040 

.0005 

0.4 

Campanula  rotundifolia,  pure. 

Do. 

179 

.1070 

.0080 

0.7 

Do. 

POLLEN    LOADS. 


127 


Table  87. — Composition  and  weight  of  pollen  loads— Continued. 

MONUMETHA  ALBIFRONS. 


Date. 

Catalogue 
No. 

Weight  of 
bee. 

Weight  of 
load. 

Load,  p.  ct. 
of  bee's 
weight. 

Composition  of  load. 

June  22 

July     8 
Do. 

26 

92 
93 

gm. 
0.1135 

.0995 
.0800 

gm. 
0.0035 

.0055 
.0050 

p.  ct. 
2 

5 
6 

Rubus  deliciosus  pure;  1  conifer 

grain. 
Rosa  acicularis,  pure. 
Do. 

08MIA    MELANOTRICHA. 

July     8 

95 
A 

gm. 
0.0247 

gm. 
0 . 0023 

p.  ct. 
9.0 

Rosa  acicularis,  pure. 
Pentstemon  gracilis,  pure. 

Panurginus  sp. 

A 

Calochortus  gunnisoni,  pure. 

PROSOPI8  varifrons. 

July  23 

131 

gm. 
0.0045 

gm. 
0.0015 

p.  ct. 
33.0 

("Geranium  caespitosum,  10  p.  ct. 
\Holodiscus  dumosus,  90  p.  ct. 

PSITHYRUS    CONSULTUS. 

A 

Solidago  missouriensis,  95  p.  ct., 
?5  p.  ct. 

Discussion.— Of  the  total  of  207  bees,  121  carried  pure  loads  of  pollen, 
i.  e.,  from  a  single  species  of  flower,  while  86  had  mixed  loads.  Three-fourths 
of  the  latter  consisted  of  2  species,  and  one-fourth  of  3  species,  a  single  load 
containing  as  many  as  4  species.  Pollen  grains  of  conifers  are  not  considered 
as  constituting  a  mixture,  since  they  were  purely  incidental.  They  may 
have  been  taken  with  the  pollen  sought  or  picked  up  separately,  but  in  no 
case  did  they  involve  a  visit  to  the  species  from  which  they  originated. 
With  the  exception  of  Halidus  pulzenus,  no  species  represented  by  4  or 
more  individuals  was  perfectly  constant  in  its  choice  of  pollen.  Apis 
mellifica  and  Andrena  crataegi  were  the  most  constant  of  these,  Bombus 
occidentalis  and  Anthophora  simillima  among  the  least  so.  The  4  genera 
represented  by  2  or  more  species  gave  the  following  ratios  between  pure 
and  mixed  loads:  Andrena  19:10,  Bombus  50:36,  Halidus  6:2,  Megachile 
12:10.  Each  of  these  contained  species  that  were  largely  or  entirely  con- 
stant on  the  one  hand,  and  those  that  were  50  per  cent  or  more  inconstant 
on  the  other. 


128 


COMPETITION  AND  CONSTANCY. 


The  only  bees  able  to  carry  a  pollen  load  amounting  to  approximately 
half  of  their  own  weight  were  species  of  Bombus;  Apis,  Colletes,  Halictus, 
and  Prosopis  coming  next  with  a  load  a  third  of  their  body-weight. 

Table  88. — Summary. 


Species. 

Maximum 
load. 

No. 
bees. 

Pure 
load. 

Mixed  load. 

2  spp. 

3  spp. 

4  spp. 

Total. 

p.  ct. 

32 
14 

32 
18 
1 
4 
5 
5 
1 
14 
27 
26 
1 
3 
1 
1 
1 
1 
4 
4 
18 
1 
1 
4 
4 
2 
2 
8 
10 
3 
2 
1 
1 
1 

28 
15 

3 
3 
1 
2 
3 
3 
1 
5 
6 
17 
1 
3 

1 

4 
3 

madronitens 

21 
13 

8 

1 
2 

1 

1 

3 
3 

4 

Anthophora  simillima 

1 

46 
61 
47 

7 
19 
9 

2 
2 

7 
8 
17 

occidentalis 

1 

1 
1 
2 
3 
4 

morrisoni 

2 

1 
1 
1 

1 

1 

4 
5 

30 

4 

33 

33 

13 

Clisodon  terminali3 

Colletes  oromontis 

Halictus  madronitens 

2 
4 

4 
6 
3 

2 

1 

1 

2 

"*3 

1 
1 
1 
3 

11 
10 

22 
6 
9 

w.  cologaster. . . . 

4 
4 

Monumetha  albifrons 

Osmia  melanotricha 

33 

1 

Total 

207 

121 

67 

18 

1 

CONSTANCY. 
Definitions. — Loew  (1884)  employed  the  term  monotropic  to  designate 
those  apids  that  visit  flowers  of  a  single  species,  oligotropic  for  those  visit- 
ing only  a  few  allied  species,  and  polytropic  for  those  that  go  indifferently 
to  very  diverse  flowers.  Robertson  further  restricted  the  terms,  designat- 
ing as  oligotropic  only  those  bees  the  females  of  which  collect  pollen 
from  a  single  species  or  from  those  of  the  same  genus  or  family  and  as 
polytropic  those  that  secure  pollen  from  flowers  of  different  families. 
Following  the  English  naturalists,  Plateau  (1901)  denoted  by  constancy 
the  behavior  of  a  polytropic  hymenopter  such  as  the  honey-bee,  which 
visits  various  species  of  flowers  during  the  season,  but  limits  its  activity 


HISTORICAL.  129 

to  the  flowers  of  a  single  species  during  one  journey  from  the  hive  or  nest. 
Detto  (1905)  pointed  out  that  constancy  may  be  used  to  refer  to  the  fact 
that  a  bee  visits  only  flowers  of  one  species  on  a  journey,  or  to  fidelity  to 
one  species  until  it  obtains  nothing  more  from  it,  when  it  goes  to  another. 
It  must  also  be  recognized  that  single  individuals  seem  to  visit  only  certain 
portions  of  very  large  or  very  floriferous  plants  and  that  they  do  not  go  to 
other  plants  of  the  same  species,  but  to  a  new  species  when  a  particular 
portion  has  been  exhausted.  Moreover,  nothing  is  known  as  to  whether  a 
bee  gives  the  preference  to  flowers  of  the  same  color  or  shade  as  those  upon 
which  it  began  to  collect.  The  term  "monodrome  constancy"  may  be 
applied  to  the  cases  where  the  bee  visits  the  flowers  of  but  one  species  during 
a  single  flight,  and  "polydrome  constancy"  to  those  where  successive 
flights  are  always  directed  to  the  same  species  as  long  as  this  yields  nectar 
or  pollen.  An  insect  that  then  goes  to  another  species  is  "temporarily 
constant"  in  contrast  to  one  that  confines  itself  chiefly  to  one  species. 

Early  observations  of  constancy. — Two  chance  observations  only 
have  been  recorded  for  the  period  before  Darwin,  one  by  Aristotle  and  the 
other  by  Dobbs  (1736).  Aristotle  stated  that  during  each  flight  the  honey- 
bee does  not  settle  upon  flowers  of  different  kinds,  but  flies,  as  it  were,  from 
violet  to  violet  and  touches  no  other  species  till  it  returns  to  the  hive. 
With  respect  to  constancy,  Darwin  (1876:415)  says: 

"All  kinds  of  bees  and  certain  other  insects  usually  visit  the  flowers  of  the  same 
species  as  long  as  they  can,  before  going  to  another  species.  It  may  be  observed  by  any 
one,  both  with  hive  and  humble  bees,  in  every  flower  garden;  not  that  the  habit  is 
invariably  followed.  Humble  and  hive  bees  are  good  botanists,  for  they  know  that 
varieties  may  differ  widely  in  the  color  of  their  flowers  and  yet  belong  to  the  same 
species.  Some  species  of  diptera  or  flies  keep  to  the  flowers  of  the  same  species  with 
almost  as  much  regularity  as  do  bees,  and  when  captured  they  are  found  covered  with 
the  pollen.  I  do  not  know  whether  lepidoptera  generally  keep  to  the  flowers  of  the 
same  species,  but  I  once  observed  many  minute  moths  apparently  eating  the  pollen 
of  Mercurialis  annua.  I  then  went  to  a  female  plant  some  yards  off  and  saw  three  of 
these  moths  light  on  the  stigmas.  It  must  not  be  supposed  from  these  several  state- 
ments that  insects  strictly  confine  their  visits  to  the  same  species.  They  often  visit 
other  species  when  only  a  few  plants  of  the  same  kind  grow  near  together.  That 
insects  should  visit  the  flowers  of  the  same  species  as  long  as  they  can  is  of  great 
importance  to  the  plant,  as  it  favors  the  cross  fertilization  of  distinct  individuals  of 
the  same  species,  but  no  one  will  suppose  that  the  insects  act  in  this  manner  for  the 
good  of  the  plant.  The  cause  probably  lies  in  the  insects  being  thus  enabled  to  work 
quicker;  they  have  just  learnt  how  to  stand  in  the  best  position  on  the  flower,  and  how 
far  and  in  what  direction  to  insert  their  proboscides." 

Kerner  (1876)  stated  that  the  bumble-bee  always  devotes  itself  to  the 
plunder  of  a  single  species  at  one  time,  but  in  commenting  on  this,  Weed 
(1884)  said  that  he  had  observed  one  bumble-bee  fly  back  and  forth  from 
Pedicularis  canadensis  to  Vicia  americana,  another  from  hyacinth  to  col- 
umbine, a  third  from  Solomon's  seal  to  dandelion,  and  a  fourth  from  vetch 
to  honeysuckle.  Forbes  (1878)  recorded  30  visits  in  succession  of  Bombus 
to  Lamium,  during  which  it  ignored  all  other  flowers,  while  Syrphus  visited 
Rubus  to  the  complete  neglect  of  Lamium.  Kronfeld  (1888:785)  observed 
a  honey-bee  that  returned  for  10  visits  to  a  bed  of  cucumbers  after  being 


130  COMPETITION  AND  CONSTANCY. 

driven  off,  though  many  species  were  in  bloom  in  the  adjacent  beds.  Three 
other  individuals  worked  solely  on  Zinnia,  though  the  same  bed  contained 
7  other  species  in  bloom,  while  a  bumble-bee  visited  exclusively  28  heads 
of  Tragopogon  in  a  10-minute  period,  in  spite  of  the  competition  of  10 
other  kinds  of  flowers. 

Bennett's  studies  of  constancy. — Bennett  (1874,  1884:175)  was 
apparently  the  first  to  make  an  extensive  study  of  the  visits  made  by  an 
insect  in  one  journey  from  the  hive,  in  the  hope  of  confirming  or  confuting 
Aristotle's  statement.  The  66  observations  made  concerned  only  the  butter- 
flies, the  syrphids,  and  apids,  and  they  appeared  to  indicate  very  different 
degrees  of  constancy.  On  the  whole,  the  butterflies  manifested  but  a  small 
degree  of  fidelity;  they  preferred  yellow  or  pink  flowers  and  showed  a 
marked  tendency  to  adhere  to  one  of  these  colors  after  starting  with 
it.  In  the  case  of  Eristalis,  it  exhibited  little  constancy  in  two  instances, 
while  in  two  others  it  confined  its  visits  to  a  single  though  different  flower. 
On  the  other  hand,  four  observations  of  Syrphus  gave  only  one  case  of 
constancy. 

Of  33  observations  made  on  various  species  of  Bombus,  4  showed  visits  to 

3  distinct  species,  while  in  6  others  the  number  of  species  noted  while  the 
insect  was  in  sight  was  2.  In  23  instances  the  bumble-bee  visited  but  a 
single  species  while  under  observation,  but  these  were  of  the  most  diverse 
kinds  and  colors.  It  was  quite  obvious  that  at  the  same  spot  different  bees  of 
the  same  species  were  visiting  different  kinds  of  flowers.  Pollen  masses 
were  examined. in  two  cases  and  found  to  consist  wholly  of  the  pollen  of  the 
flower  on  which  the  bee  was  taken.  The  honey-bee  was  constant  to  one 
species  for  5  out  of  6  observations,  the  exception  consisting  of  1  visit  to 
Scabiosa  and  9  successive  ones  to  Centaurea.  It  was  concluded  that  the 
butterflies  exhibit  little  constancy,  the  flies  greater  constancy,  while  this 
is  much  greater  for  the  bumble-bees  and  all  but  absolute  in  the  honey-bee. 
Constancy  appeared  to  increase  in  proportion  to  the  part  performed  by  the 
insects  in  carrying  pollen  from  flower  to  flower. 

Christy's  studies  of  methodic  habits.— Christy  (1884:186)  adopted 
Bennett's  methods  and  corroborated  his  general  results.  The  honey-bee 
was  found  to  be  perfectly  methodic,  not  one  individual  changing  from  one 
species  of  flower  to  another,  even  in  mixed  groups.  Among  the  bumble- 
bees one  individual  was  seen  to  visit  no  less  than  5  different  species,  3  visited 

4  species,  4  went  to  3  species,  18  to  2  species,  and  29  were  constant  to  a 
single  species.  The  Lepidoptera  were  found  to  be  much  more  constant 
than  in  Bennett's  observations,  only  3  of  the  12  individuals  going  to  a 
second  species.  It  was  observed  that  bees  were  less  constant  in  early 
spring  and  autumn,  probably  because  fewer  flowers  were  out,  a  honey-bee 
in  spring  going  twice  from  Anemone  to  Ranunculus.  Bumble-bees  proved 
more  methodic  when  visiting  blue  flowers  than  those  of  other  colors,  though 
the  results  were  not  regarded  as  conclusive. 

Mueller's  results.— Mueller  (1876)  reached  the  same  conclusions  as 
Darwin  with  reference  to  the  causes  of  constancy.  With  respect  to  the 
differences  in  the  behavior  of  male  and  female  bees  (1881),  he  found  that 


HISTORICAL.  131 

pollen  flowers  are  visited  almost  solely  by  the  females.  Many  fragrant 
honey-flowers  are  visited  by  the  males  of  certain  bees  with  especial  fond- 
ness, but  little  or  not  at  all  by  the  females  of  the  same  species.  In  cases 
where  the  females  of  a  certain  species  have  restricted  themselves  to  a  par- 
ticular flower  form  or  even  species  for  the  sake  of  rapid  and  certain  profit, 
the  males  are  not  affected  by  such  restriction  but  visit  also  other  flowers. 
Among  those  species  of  bees  that  visit  many  flower  forms,  the  females  go 
to  the  most  profitable  flowers,  the  males  to  the  easiest  or  most  fragrant. 
His  demonstration  of  the  presence  of  the  greatest  individual  differences 
in  color  preference  also  revealed  one  of  the  factors  involved  in  constancy 
(1883:275). 

Bulman's  studies.— In  a  series  of  papers  (1890,  1892,  1897,  1899) 
Bulman  dealt  especially  with  exceptions  to  the  supposed  rule  of  constancy. 

"It  is  pretty  generally  believed  that  the  bee  is  very  constant  in  its  visits  to  flowers, 
and  that  when  it  begins  with  any  particular  species  it  keeps  to  that  until  it  has  obtained 
its  load.  But  while  it  is  true  that  bees  do  show  a  considerable  amount  of  constancy 
and  often  visit  a  large  number  of  flowers  of  the  same  species  in  succession,  they  are 
far  from  possessing  that  amount  of  constancy  required  by  the  theory.  But  it  is  a 
well-established  fact  that  bees  pass  readily  from  variety  to  variety  of  the  same  species 
in  our  gardens.  They  do  not  even  confine  themselves  in  a  single  journey  to  varieties 
of  the  same  species.  In  numerous  cases  I  have  seen  bees  visit  two,  three,  or  even  four 
species  in  the  course  of  a  minute  or  two.  Hive  bees  are  much  more  constant  than  wild 
bees,  yet  they  pass  freely  from  variety  to  variety,  and  not  by  any  means  rarely  from 
species  to  species.  As  to  the  latter,  take  any  wild  bee,  and  if  you  can  follow  its  move- 
ments for  twenty  visits  or  more,  the  chances  are  something  like  ten  to  one  that  it  will 
be  seen  to  change  its  species  of  flower." 

Among  the  numerous  cases  of  inconstancy  cited,  the  most  striking  were 
those  of  a  bee  that  made  10  changes  in  27  visits  to  four  different  species 
of  geranium  and  of  a  group  of  bees  that  passed  from  Lavandula  to  Geranium, 
Leycesteria,  Epilobium,  Antirrhinum,  and  Oenothera. 

Ord's  conclusions. — Ord  (1897)  observed  the  following  routes  for  two 
honey-bees:   (1)  Cytisus  2  visits,  Primula  1,  Tremandra  1,  Eupatorium,  rose 

2,  white  2;  (2)  Caltha  7,  Ficaria  2,  Caltha  3,  Ficaria  2,  Caltha  3.  Bombus 
made  the  following  journeys:  (1)  red  Tropaeolum  1,  yellow  2,  red  1,  Viola 
1,  red  Tropaeolum  2,  yellow  Calceolaria  1,  red  2;  (2)  Geum  rivale  2,  inter- 
medium 1,  rivale  1,  intermedium  2,  urbanum  2,  rivale  6,  rivale  6,  intermedium 

3,  urbanum  1.  The  majority  of  the  apids  observed  seemed  constant  to  a 
single  species,  though  this  was  not  true  of  all  the  individuals  followed  for  a 
long  time.  Few  bees  were  able  to  resist  the  temptations  offered  by  a  garden. 
The  hive-bee  appeared  to  be  fully  as  inconstant  as  the  wild  humble-bees. 
The  most  remarkable  examples  of  constancy  were  observed  for  Salix,  Tilia, 
Calluna,  Mercurialis,  and  Ajuga.  The  transfers  seemed  especially  frequent 
when  a  number  of  related  plants  grew  together. 

Plateau  and  Perez. — The  general  results  of  Plateau's  studies  of  con- 
stancy (1901)  have  already  been  given  (p.  157).  Anthidium  and  Apis  were 
found  to  be  very  constant,  the  latter  affording  but  14  examples  of  incon- 
stancy during  three  summers,  while  Bombus  often  flew  from  one  species  to 
another  and  even  to  a  third.     P6rez  (1903:24)  objected  to  Plateau's  re- 


132  COMPETITION  AND  CONSTANCY. 

striction  of  the  term  constancy  to  polytropic  hymenoptera  and  he  extended 
it  to  apply  to  polytropic  and  oligotropic  bees  that  visit  but  one  species  of 
flower  during  a  flight.  For  the  honey-bee  constancy  is  the  usual  rule  at  any 
moment,  as  it  is  for  the  social  bees  generally,  a  fact  shown  by  the  pollen 
stored  up  in  the  hives.  It  is  likewise  the  rule  that  the  pollen-baskets  of 
bumble-bees  contain  the  pollen  of  a  single  species.  The  fidelity  of  bees  in 
general  to  a  single  species  of  flower  is  far  from  absolute,  but  it  may  be  very 
frequent.  Within  the  limits  of  observation  it  appears  only  with  respect 
to  the  collection  of  pollen  and  not  at  all  with  that  of  nectar.  Consequently, 
it  rarely  exists  with  the  males.  For  the  same  reason,  doubtless,  it  is  hardly 
to  be  found  in  hymenoptera  other  than  the  bees.  It  appears  to  exist  in 
relation  to  the  gathering  of  pollen  because  the  larva  is  less  tolerent  to  dif- 
ferences of  food  than  the  adult  (cf.  also  Peiez  1889,  1894.) 

Constancy  in  Bombus. — Wagner  (1907:38)  has  recorded  the  following 
observations  which  show  an  exceptional  degree  of  constancy  in  several 
species  of  Bombus.  Four  individuals  of  Bombus  lapidarius  made  respectively 
31,  28,  34,  and  20  visits  to  Vicia  sepium  without  going  to  other  flowers,  and 
a  fifth  sought  Lamium  album  exclusively.  Bombus  terrestris  flew  15  times 
to  Dianthus  carthusianorum  to  the  neglect  of  Vicia,  another  individual 
ignored  all  flowers  but  those  of  red  clover,  and  four  others  paid  attention 
only  to  those  of  Scabiosa;  while  the  last  visited  similarly  Melampyrum 
nemorosum.  Bombus  muscorum  went  only  to  Salvia  pratensis  on  one  day, 
in  spite  of  the  presence  of  Melampyrum,  while  on  the  next  it  flew  back  and 
forth  from  Trifolium  to  Melampyrum.  For  a  whole  day  Bombus  terrestris 
and  silvarum  worked  only  on  species  of  lilac-colored  flowers,  ignoring  all 
others.  As  a  result  of  his  study  of  the  detailed  path  followed  by  the 
bumble-bees  in  these  and  other  visits,  Wagner  reached  the  conclusion  that 
at  a  certain  distance  they  are  guided  to  flowers  by  vision  exclusively,  the 
distance  at  which  the  species  can  be  discriminated  being  determined  by  the 
size  of  the  flower,  the  inflorescence,  or  the  plant  group  itself. 

Lovell's  conclusions. — Lovell  (1914:202)  reaches  the  following  con- 
clusions as  to  the  various  types  of  constancy: 

"There  are  still  in  existence  many  intermediate  stages  between  mono-tropic,  oligo- 
tropic and  polytropic  bees.  While  many  bees  visit  a  great  variety  of  flowers,  others 
visit  only  one  family,  as  the  Compositae  or  Nymphaeaceae,  others  only  a  single  genus, 
as  Salix,  and  others  only  a  single  species,  as  the  violet,  strawberry  or  spring  beauty. 
Many  exceptions  no  doubt  occur  and  will  be  recorded  when  the  habits  of  these  bees 
have  been  more  carefully  observed.  For  instance,  I  have  often  seen  the  loosestrife 
bee  on  the  umbels  of  the  prickly  sarsaparilla.  It  is  evident  that  if  a  monotropic  bee 
extends  into  a  region  where  the  flower  it  visits  elsewhere  does  not  occur,  it  must  of 
necessity  visit  other  flowers.  Evidently  this  habit  did  not  originally  exist  among 
bees,  but  has  gradually  been  acquired. 

"We  may  sum  up  the  matter  as  follows.  All  bees  including  the  honey-bee  show  a 
strong  tendency  in  collecting  both  nectar  and  pollen  to  be  constant  to  one  species  of 
flower.  This  is  manifestly  for  the  advantage  of  both  insects  and  flowers.  In  the  case 
of  a  number  of  bees  flying  for  only  a  small  part  of  the  season,  this  habit  has  become  so 
specialized  that  they  visit  only  one  or  a  few  allied  species  of  flowers,  which  offer  an 
abundance  of  pollen  and  nectar.     As  the  honey-bee  for  a  time  restricts  its  visits  to 


HISTORICAL.  133 

the  white  clover,  so  in  like  manner  a  monotropic  bee  visits  but  a  single  kind  of  flower. 
But  in  the  former  case  the  bee  flies  throughout  the  whole  season,  while  in  the  latter 
when  the  flower  fades  the  bee's  period  of  flight  is  over." 

Kranichf eld's  observations. — Kranichfeld  (1915:39)  has  carried  out 
two  series  of  field  observations  on  the  constancy  of  the  honey-bee  to  color 
and  species.  Of  the  18  fields  studied,  15  were  being  visited  by  honeybees 
and  10  of  these  contained  plants  of  Cirsium  oleraceum.  In  these  Cirsium 
was  sought  exclusively  in  five  cases  and  chiefly  in  all  the  others,  the  only 
visits  to  other  flowers  being  to  Lathyrus  in  one  case,  Cirsium  palustre  in 
another,  and  to  Centaurea  and  Heracleum  in  the  third.  As  the  flowers  were 
almost  wholly  white  or  dull  in  color,  it  was  concluded  that  color  was  not 
decisive  in  the  choice  of  the  flowers.  In  the  second  series  the  constancy 
was  greater,  both  as  to  color  and  species,  the  exceptions  being  regarded  as 
due  to  the  behavior  of  the  young  and  inexperienced  bees.  The  other  cases 
of  inconstancy  appeared  to  be  due  to  the  confusion  of  the  honey-bees  and 
bumble-bees  by  the  presence  of  the  same  color  in  two  or  three  species. 
While  the  results  were  not  entirely  harmonious,  they  strengthened  the 
probability  that  sense  of  color  serves  to  guide  bees  and  hence  is  a  factor  in 
constancy. 

Origin  of  oligotropism. — Robertson  (1914)  ascribes  the  assumption 
of  the  oligotropic  habit  to  competition,  maintaining  that  "the  bee  fauna 
is  all  that  the  flora  will  support,  that  there  is  constant  competition  between 
bees,  and  that  natural  selection  favors  those  which  are  the  least  competitive 
in  food  habits.  The  early  maximum  flight,  the  non-competitive  pheno- 
logical  distribution,  and  the  frequent  oligotropic  habits  indicate  that  these 
bees  have  managed  to  hold  their  own  only  by  dividing  up  the  remaining  field 
and  occupying  the  most  favorable  corners  left  by  their  polytropic  compet- 
itors." On  the  contrary,  Lovell  (19142)  believes  that  only  a  part  of  the 
available  flower  food  is  gathered  by  bees,  many  plants  producing  nectar 
far  in  excess  of  the  needs  of  the  tributary  bee  population.  If  severe  com- 
petition were  to  occur,  the  oligotropic  habit  would  be  undesirable,  since 
such  a  bee  would  be  at  a  disadvantage  in  comparison  with  polytropic  spe- 
cies, unless  it  were  always  certain  to  find  the  requisite  food  supply.  In  the 
genus  Perdita,  the  tube-length  of  the  flower,  and  not  competition,  is  the 
factor  that  limits  the  visits  of  the  various  species.  It  is  concluded  that 
"certain  bees  have  become  oligotropic  because  of  the  direct  advantage 
gained,  combined  with  the  fact  that  their  flight  was  S3mchronous,  or  nearly 
so,  with  the  period  of  inflorescence  of  the  plant  to  which  they  restricted 
their  visits.  This  theory  offers  an  explanation  of  the  rise  of  oligotropism 
by  the  observation  of  existing  conditions.  There  may  be  and  often  are 
accessory  factors,  but  they  are  of  secondary  importance."  It  appears 
fairly  certain  that  Lovell  is  correct  in  assigning  the  chief  importance  to  the 
limiting  action  of  structure  and  to  the  coincidence  of  flight  and  flowering 
period,  though  there  are  doubtless  cases  in  which  competition  enters  to 
some  degree,  as  apparently  he  would  admit.  Special  studies  are  greatly 
needed  in  the  case  of  each  oligotropic  species  to  determine  the  exact  relations, 
and  these  will  afford  further  opportunity  for  the  use  of  experiment. 


134  COMPETITION  AND  CONSTANCY. 

RESUME. 
Experimental  results  in  competition. — In  the  case  of  adult  insects, 
especially  bees,  habit  is  the  controlling  factor  in  competition.  This  is 
shown  by  the  fact  that  the  standard  plant,  which  is  the  one  that  the  insect 
was  in  the  habit  of  visiting,  was  favored  in  36  cases,  while  the  bouquet, 
consisting  of  flowers  out  of  their  natural  position,  had  the  advantage  in 
but  11  cases.  Moreover,  the  difference  between  the  number  of  visitors  in 
each  experiment  was  regularly  much  greater  when  the  plant  was  preferred 
than  when  the  bouquet  was.  The  reversals  of  choice  were  caused  by  flowers 
with  a  large  amount  of  nectar,  mostly  members  of  the  rose  family,  such  as 
Rubus  strigosus,  Prunus  demissa,  and  Opulaster  opulifolius,  or  by  regular 
flowers  well-supplied  with  nectar  and  pollen,  such  as  Chamaenerium,  in 
competition  with  specialized  ones  such  as  Monarda.  In  a  few  cases,  the 
abundance  of  pollen  was  the  deciding  factor,  as  when  Rubus  deliciosus  or 
Rosa  acicularis  proved  more  attractive,  doubtless  owing  to  a  shift  in  the 
nutrition  requirements  at  the  time.  Flowers  in  vials  obtained  very  few 
visitors,  even  in  comparison  with  bouquets,  probably  because  of  the  strange- 
ness of  the  vial  itself.  The  effect  of  the  vial  is  well  exhibited  in  the  experi- 
ment where  the  two  species  of  Geranium  were  employed  reciprocally  as 
standard  plants  and  in  vials.  With  G.  richardsoni  as  the  standard  the  re- 
spective figures  were  88  and  9;  withG.  caespitosum  as  the  standard,  83  and 
10.  When  standard  roses  were  in  competition  with  roses  and  with  Cha- 
maenerium in  vials,  the  figures  were  85,  49,  and  7.  The  vials  alone  reduced 
visits  nearly  a  half,  and  a  strange  flower  in  addition  further  decreased  them 
seven  times.  In  the  case  of  natural  competition,  or  competing  bouquets, 
habit  is  partly  eliminated,  and  the  relative  attractive  power  of  the  species 
is  the  chief  factor.  This  varies,  however,  with  respect  to  the  composition 
of  the  visiting  population,  and  a  decisive  test  is  possible  only  with  young 
insects  in  which  habits  have  not  yet  been  fixed. 

Apis  mellifica  gave  the  preference  to  the  standard  plant  in  24  instances 
and  to  the  bouquet  in  4;  in  15  experiments  it  went  to  the  plant  alone. 
The  total  number  of  visitors  to  the  standard  was  972,  to  the  bouquet,  153. 
Bombus  bifarius  preferred  the  standard  in  all  of  the  9  experiments  where 
it  was  an  important  visitor,  and  went  to  it  alone  in  6  cases,  the  total  number 
of  visitors  to  standard  and  bouquet  being  206  and  20.  B.  proximus  chose 
the  plant  in  7  experiments  out  of  8,  visited  it  alone  in  6  instances,  and  222 
bees  went  to  it  in  contrast  to  48  to  the  bouquets.  B.  juxtus  was  far  less 
faithful  to  the  standard,  giving  it  the  preference  in  13  cases  out  of  19, 
visiting  it  exclusively  but  twice,  and  yielding  564  visitors  to  the  bouquets 
for  920  to  the  standards.  The  preference  as  to  species  naturally  shifted 
with  the  progress  of  the  season,  but  during  the  respective  flowering  periods 
the  marked  preferences  were  as  follows:  Apis  for  Rubus  strigosus,  Bom- 
bus for  Rubus  deliciosus,  Rosa,  Geranium,  and  Chamaenerium,  Clisodon 
for  Monarda,  Andrena  for  Opulaster  and  Prunus,  and  Osmia  for  Pentstemon. 

Effects  of  competition. — The  final  outcome  of  competition  for  pollin- 
ators in  terms  of  the  setting  of  fruit  and  the  production  of  seeds  is  difficult 
to  determine  in  nature,  owing  to  the  wide  range  of  preferences  among  the 
many  species  of  insects  usually  present.    The  only  direct  study  of  this  so 


RESUME.  135 

far  made  seems  to  be  that  of  Dodel-Port  (1882:294),  though  Lovell  (1912, 
1914)  mentions  a  number  of  observations  by  bee-keepers,  which  belong  in 
this  general  category.  Dodel-Port  found  that  two  beds  of  the  scarlet- 
runner  bean,  though  blooming  profusely,  failed  to  set  fruits  with  the  excep- 
tion of  a  single  legume,  in  spite  of  the  fact  that  elsewhere  in  Zurich  it  fruited 
abundantly.  During  this  period  repeated  observation  failed  to  reveal  a 
single  pollinating  insect  on  these  flowers,  though  honey-bees,  bumble-bees, 
butterflies,  wasps,  and  flies  were  numerous  on  the  adjacent  flowers  of 
Cerinthe,  Calendula,  Centaurea,  Bidens,  Cichorium,  etc.,  which  exercised  a 
greater  selective  power  upon  them.  Just  as  long  as  these  flowers  that  were 
richer  in  honey  continued  to  bloom,  the  bean  was  at  a  complete  disadvan- 
tage in  the  competition,  but  after  the  middle  of  August  they  began  to 
disappear  and  the  brilliance  of  the  beans  then  brought  the  visitors  to  them 
and  fruits  began  to  develop  frequently.  A  comparison  with  the  plants  of 
this  species  in  other  gardens  led  to  the  inevitable  conclusion  that  it  formed 
no  fruits  in  the  Botanical  Garden  as  a  direct  consequence  of  the  diversion 
of  the  bumble-bees  through  the  other  more  attractive  flowers. 

Constancy  as  shown  by  pollen  loads. — The  composition  of  pollen 
loads  can  only  reveal  the  behavior  of  bees  in  the  collection  of  pollen.  Too 
little  is  known  of  the  detailed  habits  of  the  various  species  of  bees  with 
respect  to  the  gathering  of  pollen  and  nectar,  and  more  exact  knowledge 
of  constancy  must  await  upon  this  among  other  matters.  The  analysis  of 
pollen  loads  showed  that  86  individuals  carried  mixed  loads  in  comparison 
with  121  carrying  pure  pollen.  With  respect  to  species,  none  represented 
by  5  or  more  individuals  was  characterized  by  pure  loads,  the  latter  being 
found  only  on  4  bees  belonging  to  Halictus  pulzenus,  on  3  of  Monumetha 
albifrons,  and  2  of  Osmia  melanotricha.  In  Apis  the  relation  of  pure  loads 
to  mixed  was  28:3,  in  Andrena  crataegi  15:3,  in  Bombus  juxtus  19:6,  and  in 
bifarius  7:5.  Variation  in  behavior  within  a  genus  is  shown  by  the  fact 
that  for  B.  occidentalis  the  ratio  was  9 :  17,  Andrena  madronitens  1 : 3,  and 
A.  vicina  2:3,  while  for  Halictus  medionitens  it  was  2:2.  It  is  clear  that 
bees  in  general  are  no  more  constant  in  the  collection  of  pollen  than  in  the 
gathering  of  nectar. 

Determination  and  designation  of  constancy. — Our  present  know- 
ledge of  the  habits  of  bees  is  inadequate  to  a  comprehensive  and  accurate 
treatment  of  constancy.  Nearly  all  those  interested  in  the  subject  have 
defined  constancy  in  different  terms  and  the  studies  that  bear  directly  on 
this  relation  have  been  so  few  and  fragmentary  that  further  advance  must 
await  special  investigations  which  are  at  once  extensive  and  intensive. 
These  must  take  account  of  behavior  with  respect  to  both  pollen  and 
nectar,  the  differences  between  individuals,  sexes,  ages,  species,  etc., 
single  flights  and  those  made  on  the  same  day,  and  on  different  days 
and  at  different  parts  of  the  flowering  period  of  preferred  species.  Further- 
more, they  must  employ  experiment  to  vary  conditions  in  a  definite  manner 
in  order  to  test  habit  under  new  circumstances  and  to  furnish  quantitative 
results,  which  will  permit  the  expression  of  the  degree  of  constancy  for 
individual  or  species  in  numerical  terms. 


4.  PRINCIPLES  AND   CONCLUSIONS. 

INTRODUCTORY. 

Nearly  the  entire  history  of  experimental  pollination  is  reflected  in  the 
writings  of  Plateau  and  the  papers  called  forth  by  his  results.  His  were  the 
first  researches  in  this  field  and  for  thirty-five  years  his  classic  experiments 
were  the  outstanding  features  of  its  development.  Indeed,  he  and  his 
critics  occupied  the  stage  until  the  last  decade,  which  has  been  marked  by 
researches  not  genetically  related  to  his.  Thus,  while  Plateau  is  the  dom- 
inant figure  almost  throughout,  it  is  helpful  to  divide  the  period  of  develop- 
ment into  four  stages,  as  follows;  (1)  early  experiments  of  Plateau  and  others, 
(2)  main  researches  of  Plateau,  (3)  related  studies  and  critiques,  (4)  recent 
investigations.  In  the  hope  of  providing  a  comprehensive  and  exhaustive 
account  of  experimental  pollination,  abstracts  are  given  in  detail  of  all 
experimental  studies,  and  of  such  critical  discussions  as  those  of  Knuth, 
Kienitz-Gerloff,  and  others.  Because  of  their  significance  and  their  frequent 
inaccessibility,  the  papers  by  Plateau  have  been  summarized  with  especial 
fullness.  The  historical  section  is  followed  by  an  extended  resume  of  results 
and  conclusions,  examined  in  the  light  of  the  present  researches. 
EARLY  EXPERIMENTS  OF  PLATEAU  AND  OTHERS. 

Artificial  flowers. — The  stimulus  for  Plateau's  first  experiments  came 
from  an  observation  reported  by  Vallete  (1875),  according  to  which  an 
individual  of  Macroglossa  stellatarum,  which  had  entered  through  the 
window,  tried  vainly  to  plunge  its  tongue  in  the  flowers  of  a  tapestry, 
"passing  from  one  bouquet  to  another  and  choosing  skillfully  the  flowers 
that  it  sought  to  probe."  The  unfavorable  comments  called  forth  by  this 
statement  led  Plateau  to  come  to  its  defense  with  his  study  of  response  to 
artificial  flowers  (1877:535).  The  latter  consisted  of  red  and  yellow  roses, 
yellow  Ranunculus,  and  variegated  Convolvulus,  which  were  made  to  resem- 
ble natural  flowers  as  closely  as  possible.  They  were  placed  in  the  garden 
among  plants  of  Viola,  Pulmonaria,  Primula,  Fritillaria,  Crocus,  Hyacinthus, 
and  Arabis,  of  which  the  latter  was  almost  alone  in  being  visited  by 
insects,  chiefly  Vanessa  and  A  pis.  During  two  hours  of  observation  no 
visitor  came  to  the  artificial  flowers,  though  a  butterfly  passed  near  one. 
When  the  same  artificial  flowers  were  placed  in  a  bed  of  Hyacinthus  or  of 
Arabis,  or  the  latter  mixed  with  artificial  flowers  of  its  own  kind,  the  results 
were  the  same,  only  a  single  honey-bee  hesitating  for  a  moment  above  them. 
Moreover,  when  a  drop  of  honey  was  placed  in  the  center  of  each  false 
Arabis,  no  visitors  alighted  on  the  flowers,  although  Anthophora  frequently 
poised  above  them  as  though  drawn  by  the  odor.  Two  showy  beds  of  arti- 
ficial flowers  of  violets,  pansies,  marsh  marigolds,  roses,  buttercups,  etc., 
were  placed  in  a  sunny  sward,  but  of  the  Anthophora,  Apis,  Bombus, 
Pieris,  and  Vanessa  flying  about,  only  the  latter  noticed  them  in  the  least 
and  then  but  momentarily.  On  the  same  day  branches  of  a  cherry  in  full 
bloom  were  provided  with  flowers  made  to  resemble  the  cherry  and  white 
lilac,  but  the  bees  visited  only  the  natural  ones.  When  imitation  roses, 
white,  pink,  and  red  in  color,  were  mixed  with  natural  ones,  Apis, 
Bombus,  Trichius,  and  various  flies   showed    complete  indifference  to  the 

136 


EARLY  EXPERIMENTS   OF  PLATEAU   AND   OTHERS.  137 

former,  though  Syrphus  poised  for  some  time  above  a  false  rose  and  Pieris 
wheeled  to  make  a  small  circle  above  a  group.  A  shoot  of  Aucuba  without 
natural  flowers  was  furnished  with  artificial  ones  of  a  lively  color,  but 
drew  no  visitors  during  a  half-hour  of  observation.  In  the  final  experiment, 
a  large  number  of  brilliant  artificial  flowers  was  placed  in  one  group  in  the 
center  of  a  lawn  surrounded  by  a  garden  in  full  bloom.  Although  many 
bees,  butterflies,  and  flies  were  working  on  the  latter,  but  two  individuals 
of  Pieris  came  to  inspect  the  imitation  flowers. 

In  conclusion,  Plateau  stated  that  the  bright  colors  of  flowers  attract  but 
a  small  number  of  insects,  chiefly  diurnal  Lepidoptera,  a  group  in  which 
instinct  is  but  feebly  developed.  Insects  are  able  to  perceive  differences 
between  natural  and  artificial  flowers  that  escape  the  observer  who  is  not 
forewarned,  differences  sufficiently  great  to  permit  no  error  and  even  to 
excite  distrust.  In  their  flight  from  a  distance  to  the  flower  sought,  insects 
are  probably  guided  by  some  other  sense  than  sight  alone.  Thus,  he  was 
led  to  draw  conclusions  which  were  exactly  the  opposite  of  what  he  expected. 
He  disclaimed  any  desire  to  render  a  final  judgment,  but  regarded  the  meth- 
ods employed  as  worthy  the  attention  of  those  engaged  in  the  study  of 
pollination. 

Nectaries. — Bonnier  (1878:5)  challenged  the  prevailing  view  of  the 
fundamental  importance  of  floral  nectaries  in  pollination,  scrutinizing 
in  detail  the  evidence  adduced  by  the  enthusiastic  students  of  floral  biology. 
He  pointed  out  that  the  development  of  spurs  in  flowers  is  not  necessarily 
in  accord  with  the  presence  of  nectar,  and  that  this  is  likewise  true  of 
scales,  hairs,  and  other  devices  for  protecting  the  nectar.  A  considerable 
list  was  given  of  flowers  of  inconspicuous  color  that  are  abundantly  visited 
by  insects,  and  a  reciprocal  list  of  bright-colored  flowers  little  or  not  at  all 
visited  because  of  the  lack  of  nectar.  The  view  of  Mueller  that  the  vis- 
ibility of  the  flower  is  proportional  to  insect  visits  and  to  the  development 
of  floral  adaptation  was  tested  by  means  of  related  species  of  different 
color.  The  greenish-white  flowers  of  Teucrium  scorodonia  were  visited 
by  13  honey-bees  in  the  same  time  that  3  went  to  the  red  ones  of  T.  chamae- 
drys,  while  4  species  of  Allium  with  a  nearly  equal  attractive  surface  re- 
ceived respectively  6,  4,  5,  and  15  visits.  In  the  case  of  Althea  rosea  an 
equal  number  of  red,  rose,  and  white  flowers  gave  14,  13,  and  13  visits 
by  honey-bees  and  4,  3,  and  4  visits  by  bumble-bees  respectively.  Ob- 
servations were  reported  for  a  number  of  other  species,  and  a  special  test 
of  response  to  color  was  made  by  means  of  rectangles  colored  red,  green, 
yellow,  and  white,  provided  with  an  equal  amount  of  honey  and  placed  at 
equal  distances  from  the  hives.  The  maximum  number  of  visits  for  any 
one  minute  was  78  for  yellow  during  the  ninth  minute,  90  and  93  respec- 
tively for  red  and  green  during  the  tenth  minute,  and  85  for  white  during  the 
eleventh  minute,  the  totals  being  549,  621,  640,  and  652.  The  conclusion 
was  reached  that  there  is  no  agreement  between  the  development  of  colors 
and  that  of  nectar,  that  in  the  same  conditions  the  flowers  with  brightest 
colors  are  not  the  most  visited  by  insects,  and  the  visibility  of  flowers 
is  not  proportional  to  their  adaptation  to  cross-fertilization;  in  short, 
insects  go  in  greatest  number  where  the  nectar  is  most  abundant,  the  rich- 
est in  sugars,  and  easiest  to  obtain. 


138  PRINCIPLES  AND  CONCLUSIONS. 

The  view  that  the  male  flowers  are  more  visible  than  the  female  in 
diclinic  nectariferous  flowers  was  tested  by  observations  of  Salix,  Ribes, 
Asparagus,  and  Bryonia.  The  number  of  visitors  was  so  nearly  equal  that 
it  was  stated  that  in  such  flowers  the  bees  do  not  go  first  to  the  staminate 
and  then  the  pistillate,  and  that  the  former  do  not  possess  a  greater  vis- 
ibility. The  development  of  spots  and  stripes  on  the  corolla  was  thought 
not  to  be  correlated  with  the  nectar  or  the  presence  of  a  large  corolla, 
which  is  independent  of  the  frequent  visits  of  insects.  The  development 
of  perfume  in  the  flower  and  that  of  nectar  are  not  in  agreement.  The  same 
flower  can  be  visited  in  several  different  ways  by  the  same  insect,  indicating 
that  there  is  no  reciprocal  adaptation  between  them,  as  is  shown  also 
by  the  fact  that  insects  continue  to  visit  flowers  after  the  corolla  has  fallen. 
Insects  are  able  to  secure  nectar  from  the  flower  without  effecting  fecund- 
ation, as  is  especially  true  of  the  large  number  of  flowers  that  are  robbed  by 
bees.  The  visitors  to  the  same  species  differ  in  accordance  with  the  var- 
iations in  the  amount  of  nectar.  Furthermore,  undesirable  visitors  are  not 
excluded  by  odor,  form,  or  by  the  time  or  place  of  blooming.  In  sum- 
marizing it  was  stated  that  it  is  impossible  to  admit  that  all  the  features 
of  flowers  are  designed  to  attract  insects  in  furnishing  them  nectar,  and 
thus  bringing  about  cross-fertilization.  One  can  not  admit  that  there  may 
be  reciprocal  adaptation  between  flowers  and  insects,  since  the  observed 
facts  do  not  accord  with  the  imaginary  hypotheses.  Finally,  the  modern 
theory  as  to  the  role  of  the  nectary  seems  to  be  inadequate. 

It  is  obvious  that  Bonnier's  conclusions  were  much  more  sweeping 
than  his  evidence  warranted,  and  hence  it  is  not  strange  that  he  should 
have  been  severely  criticized  by  Mueller  (1880:219),  who  declared  that 
Bonnier,  in  his  blind  and  presumptuous  endeavor  to  destroy  one  of  the 
most  comprehensive  and  best-grounded  of  theories  by  childish  weapons, 
had  only  succeeded  in  bringing  to  it  new  support.  In  spite  of  this,  however, 
he  deserves  much  credit  for  pointing  out  some  of  the  serious  weaknesses 
of  a  theory  which  attempted  to  explain  the  most  insignificant  features 
of  the  flower  as  both  cause  and  effect  of  insect  pollination. 

Color  sense  of  bees. — Lubbock  (1882:291)  studied  the  response  of 
honey-bees  to  color  by  means  of  paper  slips  and  glass  slides  provided  with 
honey.  The  latter  was  placed  on  blue  and  on  orange  paper  and  a  bee 
brought  to  the  former.  After  she  had  returned  twice  the  papers  were 
transposed,  but  she  still  went  to  the  blue  paper,  as  she  did  also  when 
the  papers  were  again  transposed  after  three  visits  to  the  blue.  Similar 
results  were  obtained  two  days  later,  in  which,  as  the  bee  returned  to 
the  usual  place,  now  occupied  by  the  orange  slip,  she  started  to  alight 
and  then  darted  off  to  the  blue.  Experiments  of  the  same  sort  were  made 
at  various  times,  and  agreed  in  showing  that  bees  return  to  the  color  to 
which  they  have  been  accustomed. 

To  determine  whether  there  was  a  preference  for  one  color  over  another, 
Lubbock  made  use  of  microscope  slides  on  which  were  pasted  slips  of  paper 
colored  respectively  blue,  green,  orange,  red,  white,  and  yellow.  These 
were  placed  on  a  lawn  about  a  foot  apart  and  on  top  of  each  was  put  a 
second  slide  with  a  drop  of  honey;  with  them  was  also  placed  a  slide  of 
plain  glass  with  honey.    After  a  marked  bee,  trained  to  come  for  honey, 


EARLY  EXPERIMENTS   OF   PLATEAU   AND   OTHERS.  139 

had  sipped  for  a  quarter  of  a  minute,  the  slide  with  honey  was  moved  so 
that  she  flew  to  another  slide.  This  was  next  taken  away,  and  so  on,  until 
she  was  induced  to  visit  all  the  drops  before  returning  to  the  hive.  While 
she  was  absent,  all  the  upper  glasses  with  honey  were  transposed  and  the 
colored  slips  also  moved,  so  that  position  could  not  influence  selection 
by  the  bee.  The  record  was  made  by  noting  the  order  in  which  the  bee 
went  to  the  different  colors.  The  experiment  was  repeated  a  hundred 
times  with  the  use  of  two  different  hives  at  different  places  and  the  obser- 
vations extended  over  some  time  in  order  to  work  with  different  bees  and 
under  varied  conditions.  The  first  day's  results  gave  a  decided  preference 
for  blue;  white,  yellow,  and  green  were  nearly  equal,  followed  by  orange 
and  red  also  about  equal,  with  the  plain  glass  last.  In  the  next  series, 
bees  had  been  trained  for  three  weeks  to  come  to  a  particular  spot  on  the 
lawn  by  placing  honey  on  a  piece  of  plain  glass.  In  spite  of  the  advantage 
thus  given  the  latter,  blue  was  again  first,  followed  at  some  distance  by 
white,  and  this  by  yellow,  red,  green,  orange,  and  plain  glass. 

Bonnier's  results  to  the  contrary  were  regarded  as  inconclusive,  since 
the  colors  were  largely  covered  up  by  the  bees  and  since  the  presence  of 
so  many  would  attract  their  companions.  Moreover,  he  omitted  blue  and 
his  squares  were  all  colored,  the  absence  of  colorless  checks  being  especially 
serious. 

Response  to  detached  petals.— Mueller  (1883:273)  regarded  Lubbock's 
results  as  inconclusive,  since  he  did  not  use  the  natural  colors  of  the  flower 
and  did  not  give  the  bee  a  distinct  choice  between  two  plates  differing  in 
color  alone.  To  obviate  these  difficulties  Mueller  made  use  of  detached 
petals  placed  between  glass  slides  which  were  cemented  at  the  edges, 
so  that  the  odor  could  not  be  effective.  A  drop  of  honey  was  placed  on 
each  test-object  thus  prepared.  As  a  rule,  petals  of  two  distinct  colors 
were  submitted  to  the  choice  of  bees  that  had  been  marked  and  accustomed 
to  coming  for  honey  on  glass  slides.  In  their  color  preference  different 
honey-bees  exhibited  marked  individual  response,  one  showing  equal 
liking  for  both  colors,  another  a  preference  for  one,  and  a  third  for  the  other. 
Thus,  while  the  total  number  of  visits  made  by  a  group  of  6  bees  to  the  purple 
of  a  rose  and  the  blue  of  a  cornflower  was  the  same  for  each,  only  three 
bees  were  equally  sympathetic  to  them,  the  other  three  visiting  them 
in  the  following  ratios:  10:14,  5:3,  and  3:1.  In  the  case  of  the  fire-red 
of  nasturtium  and  the  violet  of  the  pansy,  seven  of  eight  bees  preferred  the 
latter,  most  of  them  very  decisively,  and  but  one  the  former,  also  very 
distinctly,  viz,  10:3.  Individual  bees  also  differed  in  the  constancy  of 
their  response  to  related  colors,  two  preferring  honey-yellow  to  brilliant 
yellow  throughout  the  period  of  experiment,  and  the  other  two  choosing 
the  one  in  the  first  half  and  the  other  in  the  second.  Bright  colors,  bril- 
liant yellow  and  orange,  fire-red,  scarlet,  are  less  pleasing  to  the  honey- 
bee than  the  softer  colors  with  which  the  bee-flowers  are  adorned,  viz, 
white,  honey-yellow,  rose,  pink-red,  violet,  and  blue.  The  preference 
for  bright  yellow  and  honey-yellow  was  48:78,  for  the  former  and  white 
21:48,  for  brilliant  orange  and  rose  22:71,  and  26:77,  for  fire-red  and 
violet  29:80,  for  scarlet  and  rose  9:55,  for  scarlet  and  pink  34:69,  and  for 
scarlet  and  blue  13:78. 


140  PRINCIPLES  AND  CONCLUSIONS. 

The  least  attractive  of  all  the  colors  of  true  bee-flowers  is  glaring  yellow, 
the  ratio  between  this  and  yellow-white  being  35:68,  with  pink-red  27:74, 
with  purple  42:62,  with  indigo-blue  28:56,  and  with  violet  24:78,  while 
chrome-yellow  and  cobalt-blue  gave  11:40.  White  and  yellowish- white 
were  visited  about  as  readily  as  many  shades  of  purple  or  even  more  so, 
but  less  readily  than  blue  or  violet;  for  example,  white  against  dark- 
purple  gave  a  ratio  of  7:30,  and  against  sky-blue  36:64,  while  yellowish- 
white  and  purple  gave  52:49,  with  blue  18:25,  and  with  violet  11:24. 
Blue  is  either  preferred  to  red,  or  the  two  are  equally  attractive,  in  accord- 
ance with  the  particular  shades  employed;  thus,  violet-blue  in  competition 
with  dull-purple  gave  61:31,  sky-blue  and  bright  purple  45:36,  sky-blue 
and  rose  57:54,  cornflower  blue  and  purple  52:52,  and  impure  violet-blue 
and  dark-purple  57:57.  A  pure  deep  blue  excels  violet  in  attraction  in 
the  proportions,  50:35  and  81:67.  In  its  attraction  for  the  honey-bee 
violet  excels  all  other  flower  colors  except  blue.  Among  the  brilliant  flower 
colors,  bright  yellow  is  the  most  attractive  to  bees,  giving  with  scarlet 
the  ratio  50:29,  and  with  bright  orange  42:31.  The  green  of  leaves  is  less 
pleasing  to  honey-bees  than  the  colors  of  bee-flowers,  giving  in  competition 
with  rose  75:33,  but  it  is  more  attractive  than  scarlet,  45:40  or  orange 
57:46.  As  a  result  of  field  observations,  Kranichfeld  (1915:40)  has  come 
to  the  conclusion  that  the  color  preference  demonstrated  by  Mueller's 
experiments  does  not  obtain  in  the  normal  visits  of  bees  to  flowers  (see 
p.  133). 

Color  preference  of  nocturnal  moths. — Gratacap  (1883:791)  made 
cylinders  of  variously  colored  tissue-papers  and  drew  them  over  common 
kerosene  lamps  with  gas  chimneys  in  order  to  test  the  color  perceptions 
of  night-flying  insects.  The  colored  lights  were  first  placed  in  a  row  at  long 
distances  from  each  other,  but  this  arrangement  seemed  defective  by  reason 
of  the  fact  that  the  brilliancy  of  the  light  first  visited  interfered  with  the 
visitor's  freedom  of  choice  between  that  color  and  another  that  reached 
it  but  dimly.  The  lights  were  next  arranged  in  a  square,  at  first  in  such 
manner  that  the  circles  of  light  touched  each  other,  but  later  so  that  they 
overlapped.  Since  this  did  not  permit  an  exactly  equal  choice,  the  final 
plan  was  to  make  use  of  but  two  lamps  at  a  time.  The  need  of  causing  the 
insect  to  choose  instantly  between  the  colors  before  it  reached  either  arose 
from  the  infatuation  produced  by  the  lights,  preventing  the  insect  from 
freeing  itself  except  in  an  accidental  manner.  The  results  indicated  the 
absence  of  marked  preference  for  certain  colors  over  others,  and  demon- 
strated the  almost  invariably  greater  charm  of  the  white  lantern,  which 
on  account  of  its  translucency  appeared  more  brilliant  than  the  colored  ones. 

Response  to  color  without  antennae. — Forel  (1886:24)  considered 
that  the  ingenious  and  patient  studies  of  Lubbock  had  demonstrated  the 
ability  of  bees  and  wasps  to  distinguish  colors  and  at  the  same  time  a  feeble 
sense  of  smell  in  the  former.  While  this  seemed  to  be  contradicted  by 
the  experiments  of  Plateau  with  artificial  flowers,  such  negative  results 
were  regarded  as  of  less  value,  especially  since  other  factors  rendered  the 
investigation  incomplete.  Above  all,  it  is  possible  and  even  probable 
that  an  imitation  exact  to  our  eyes  may  affect  those  of  an  insect  so  that 


EARLY  EXPERIMENTS   OF   PLATEAU   AND   OTHERS.  141 

it  will  perceive  differences  not  apparent  to  us.  Moreover,  Plateau  failed 
to  take  odor  into  account,  though  this  is  of  less  importance,  and  finally, 
Lubbock  has  shown  that  bees  and  wasps  are  so  controlled  by  habit  that 
new  flowers  would  attract  them  less  than  those  to  which  they  were  habit- 
uated. To  determine  the  attraction  exerted  by  color,  Forel  cut  the  antennae 
of  6  individuals  of  Bombus  terrestris  at  the  base  and  released  them.  At  the 
end  of  5  minutes  a  male  returned  and  visited  10  flowers  of  bindweed  in 
succession,  each  time  flying  directly  to  the  flower  without  hesitating  a 
second.  It  was  caught,  the  antennae  examined  to  confirm  their  complete 
absence,  and  then  released,  when  it  made  a  single  circuit  in  the  air  and 
returned  immediately  to  the  flowers,  to  visit  them  as  before.  In  the  case 
of  other  bumble-bees  the  front  of  the  head  was  cut  away  as  far  as  the  com- 
pound eyes  and  the  remainder  of  the  lower  lip  and  the  entire  pharynx 
removed.  Nevertheless,  the  bees  thus  mutilated  flew  actively,  saw,  and 
moved  their  antennae;  when  released  they  returned  to  the  flowers,  but 
remained  only  an  instant  in  each,  since  they  were  unable  to  suck  nectar. 
At  the  same  time  several  of  the  bees  without  antennae  came  again  to  the 
bindweeds,  flying  from  one  to  the  other  with  more  precision  if  possible 
than  those  with  the  antennae  intact.  Two  days  later  several  of  the  mutilated 
bees  were  again  found  on  the  flowers,  visiting  them  with  an  astonishing 
rapidity  and  precision.  When  the  antennae,  the  front  part  of  the  head 
and  the  pharynx  were  removed  from  males  of  Bombus  pratorum,  one  of 
these  made  a  turn  and  flew  directly  back  to  the  Veronica  it  had  been  visit- 
ing, seeking  vainly  to  secure  nectar  from  it  as  well  as  from  the  bindweed. 
A  second  shortly  returned  and  behaved  in  the  same  manner,  while  the  small 
females  thus  treated  did  not  come  back,  apparently  because  of  their  greater 
intelligence.  A  wasp,  Polistes  gallicus,  treated  in  the  same  way,  behaved 
similarly,  returning  to  the  mignonette  in  a  fruitless  quest. 

Forel  noted  that  the  loss  of  the  antennae  in  these  cases  seemed  to  increase 
instead  of  decreasing  the  precision  of  flight.  The  insects  no  longer  balanced 
to  the  right  and  left  before  alighting,  but  flew  in  a  straight  line  to  the 
flower  and  landed  immediately,  the  difference  in  behavior  before  and  after 
the  removal  of  the  antennae  being  especially  striking  in  Vespa.  All  this 
seems  to  indicate  that  the  balancing  in  flight  enables  these  insects  to  smell 
certain  substances  with  their  antennae,  which  explains  why  this  movement 
is  more  marked  with  the  wasps  which  smell  readily  and  see  less  well  than 
with  the  bees,  where  the  reverse  is  true.  The  experiments  were  regarded 
as  demonstrating  clearly  that  it  is  the  compound  eyes  alone  that  direct 
flies,  butterflies,  beetles,  dragon-flies,  bumble-bees,  and  wasps  in  their 
flight.  It  is  by  means  of  these  organs  alone  that  these  insects  distinguish 
colors  on  the  wing,  as  well  as  objects,  especially  when  they  are  moving, 
distances,  and  pathways  through  the  air.  Odor  can  attract  certain  winged 
insects  in  a  certain  direction,  but  without  eyes  they  could  not  find  their 
way. 

Perception  of  form. — An  individual  of  Vespa  germanica  was  placed  by 
Forel  on  a  circle  of  white  paper  3  cm.  wide,  spread  with  honey.  After 
taking  its  fill,  the  wasp  flew  away,  but  returned  at  once  directly  to  the 
white  circle  and  again  sipped  the  honey.    The  white  paper  was  then  re- 


142  PRINCIPLES  AND  CONCLUSIONS. 

placed  by  one  without  honey,  while  it  was  moved  to  one  side  at  a  distance 
of  2  inches.  The  wasp  returned  to  the  original  place  occupied  by  the  disk 
without  honey,  and  finding  nothing  there,  rose  a  little,  balanced  two  or 
three  times,  and  went  to  the  paper  with  honey.  During  its  absence  honey 
was  placed  upon  a  cross  of  white  paper  about  11  cm.  long,  and  this  with 
the  empty  white  disk  was  placed  near  the  spot  last  visited.  Upon  returning 
the  wasp  soon  found  the  honey,  probably  because  the  cross  was  not  suf- 
ficiently different,  and  it  was  replaced  by  a  white  band.  On  the  next, 
visit  the  wasp  flew  direct  to  the  white  disk  and  searched  a  long  time  for 
honey,  and  then  went  to  the  original  place  in  vain.  It  repeated  this  before 
it  was  able  to  find  the  honey  in  consequence  of  repeated  searching.  On  the 
morrow  the  wasp  came  twice  to  take  nectar  from  the  cross,  when  it  was 
caught  and  the  antennae  removed.  It  flew  away,  but  returned  in  a  half- 
hour  to  sip  upon  the  same  cross.  After  its  departure  a  similar  cross  with- 
out honey  was  placed  at  one  side,  and  on  the  other  a  band  with  honey, 
the  original  cross  then  being  taken  away.  The  wasp  returned,  flew  directly 
to  the  cross,  and  alighted  in  the  middle,  hunting  vainly  during  a  rather 
long  time.  Then  it  began  to  search,  apparently  remembering  that  the  papers 
had  been  frequently  transposed,  and  after  passing  two  or  three  times 
within  a  few  millimeters  of  the  honey,  finally  found  it  after  the  tongue 
practically  touched  it. 

A  bumble-bee,  trained  to  take  honey  from  a  blue  disk,  first  flew  to  one 
without  honey,  but  taken  again  to  the  former,  returned  to  it  several  times 
without  error.  The  blue  disk  was  next  replaced  by  a  blue  band,  and  a 
disk  alone  put  at  a  distance  of  three  inches.  The  bee  then  flew  straight 
to  the  disk,  but  made  only  one  turn  before  going  to  the  band  with  nectar. 
He  was  returned  to  the  disk  with  nectar,  which  he  visited  several  times. 
Two  hours  later  this  was  replaced  by  the  band  with  honey,  and  a  disk  without 
was  put  at  6  cm.  This  time  the  bee  came  first  to  the  original  place  now  occu- 
pied by  the  band,  but  scarcely  hesitated,  failing  to  note  the  honey,  and  flew 
to  the  empty  disk,  which  he  searched  thoroughly  two  or  three  times,  finally 
going  to  the  band  with  the  honey.  When  a  red  disk  with  honey  was  sub- 
stituted for  the  blue,  and  an  empty  blue  one  placed  at  4  or  5  inches,  the  bee 
each  time  went  straight  to  the  latter  and  could  not  find  the  honey  on  the 
red  disk,  even  though  it  was  in  the  original  place.  Once  found  by  chance, 
he  hardly  tasted  it,  so  much  was  he  obsessed  by  the  association  of  "honey 
and  blue,"  before  he  again  began  his  search  upon  the  blue  disk,  without 
returning  to  the  honey  on  the  red  one.  This  was  explained  by  the  fact 
also  that  bumble-bees  have  much  poorer  memories  than  wasps,  since 
several  visits  are  necessary  to  enable  them  to  find  a  place  without  hesi- 
tation, while  one  suffices  for  the  wasp. 

Consequently,  the  influence  of  color  was  regarded  as  of  the  greatest 
significance.  The  bee  did  not  know  enough  to  find  the  honey  on  the  red 
disk  when  he  was  brought  to  touch  it;  he  still  sought  it  on  the  blue  with 
a  perseverance  but  little  intelligent.  It  is  evident  that  he  perceived 
the  color  in  a  fashion  infinitely  more  intense  than  the  form  of  the  paper. 
On  the  contrary,  as  Lubbock  has  shown,  while  the  bumble-bees  and  honey- 
bees distinguish  colors  especially  well,  wasps  pay  little  attention  to  them, 
but  recognize  places  admirably,  the  one  employed  going  direct  to  a  red 


EARLY  EXPERIMENTS   OF   PLATEAU   AND   OTHERS.  143 

disk  in  the  place  formerly  occupied  by  the  blue  one,  and  paying  no  heed 
to  the  latter  at  one  side.  On  the  other  hand,  when  the  disk  is  moved  a 
foot  from  the  former  place,  the  wasp  is  usually  unable  to  find  it,  while 
the  bee  locates  it  quickly  by  the  color.  The  fact  that  wasps  guide  them- 
selves so  well  when  deprived  of  antennae,  without  distinguishing  colors 
very  clearly,  is  one  of  the  best  proofs  that  they  see  the  forms  and  contours 
of  objects,  further  evidence  being  afforded  by  the  fact  that  they  can  not 
direct  themselves  when  their  eyes  are  covered  with  varnish. 

Response  of  wasps  to  color. — In  their  classic  experiments  with  wasps 
(1887:105),  the  Peckhams  carried  out  experiments  upon  the  response  to 
color,  largely  with  the  idea  of  verifying  Lubbock's  conclusions.  Their 
results  were  somewhat  at  variance  with  his,  however,  as  they  tended  to 
prove  that  wasps  rely  very  greatly  upon  color  for  their  guidance.  This 
divergence  may  be  explained  in  part  by  the  fact  that  they  worked  with 
large  numbers,  500  sometimes  passing  into  and  out  of  the  nest  in  5  minutes, 
and  that  the  presence  of  two  observers  increased  the  accuracy.  At  the 
outset  a  hole  4.5  inches  in  diameter  was  cut  in  a  sheet  of  bright-red  paper 
about  24  by  20  inches  in  extent,  and  the  latter  was  placed  above  the  nest 
in  such  a  way  that  the  entrance  was  not  at  all  impeded  and  could  be  plainly 
seen  from  above.  The  returning  wasps  did  not  enter,  but  circled  over  the 
paper,  seeming  greatly  excited,  until  one  more  intelligent  or  venturesome 
flew  in  and  the  others  gradually  followed.  In  the  course  of  3  hours  all  of 
them  became  accustomed  to  the  paper  and  worked  as  usual.  Two  days 
later  a  blue  paper  was  substituted  and  this  produced  as  much  confusion 
as  before,  though  the  wasps  became  used  to  it  in  a  little  more  than  2  hours. 
The  next  day  the  blue  paper  was  removed  and  a  cage  full  of  wasps  released 
at  some  distance;  an  hour  afterward  25  or  30  wasps  were  found  buzzing 
about,  apparently  not  knowing  how  to  get  into  the  nest,  though  they  en- 
tered at  once  as  soon  as  the  blue  paper  was  replaced.  When  a  yellow  paper 
was  substituted  for  the  blue,  130  wasps  noticed  the  change  within  a  period 
of  10  minutes,  circling  around  the  nest  several  times  before  entering,  while 
8  seemed  not  to  notice  it.  After  an  hour's  exposure,  70  out  of  100  wasps 
recognized  the  change,  but  after  the  paper  had  been  over  the  nest  for  3 
working  hours,  only  8  out  of  200  hesitated  before  entering.  The  sub- 
stitution of  a  light-green  paper  with  yellowish  reflections  for  the  yellow  one 
produced  a  response,  but  it  was  not  nearly  so  marked,  100  out  of  172 
wasps  noting  it,  but  to  a  smaller  degree. 

When  three  dark-red  nasturtiums  were  placed  on  yellow  paper  2  inches 
from  the  hole,  46  of  146  wasps  noticed  them  by  flying  to  them  and  almost 
alighting  during  a  period  of  5  minutes,  while  29  of  126  noticed  them  in 
the  next  5  minutes.  With  the  substitution  of  California  poppies  of  a  yellow 
color  for  the  red  nasturtiums,  the  number  was  much  smaller,  being  but 
5  per  hundred  for  10  minutes  instead  of  28  per  hundred,  the  previous 
rate.  Replacing  the  dark-red  flowers  brought  the  rate  again  to  18  per 
hundred.  To  eliminate  the  effect  of  perfume,  3  light  yellow  nasturtiums, 
which  matched  the  paper  even  more  closely  than  the  poppies,  were  em- 
ployed; these  received  but  3  notices  per  hundred,  proving  that  the  dif- 
ferences observed  were  due  to  color  and  not  to  odor. 


144  PRINCIPLES  AND  CONCLUSIONS. 

Being  satisfied  that  the  wasps  distinguished  colors  and  were  disturbed 
by  a  change  from  one  to  another,  an  endeavor  was  made  to  determine 
more  exactly  the  impression  made  by  a  particular  color.  After  the  red 
paper  had  been  over  the  nest  for  24  hours,  it  was  moved  a  foot  and  half 
to  the  south  and  a  blue  one  put  in  its  place,  in  order  to  determine  whether 
any  of  the  returning  wasps  would  enter  the  hole  in  the  red  paper,  to  which 
they  were  accustomed,  instead  of  going  to  the  real  entrance  through  the 
blue  paper.  For  convenience  the  blue  was  designated  as  the  true  and  the 
red  as  the  false  entrance.  In  the  first  10  minutes,  76  wasps  went  into  the 
true  entrance,  of  which  54  first  hovered  over  the  false  and  about  half  of 
which  actually  entered  it  and  explored  the  grass  below.  Some  of  the  lat- 
ter, not  finding  the  entrance  here,  flew  away  entirely,  and  most  of  those 
that  entered  the  true  one  directly  did  not  pass  above  the  red  paper  in  so 
doing.  In  the  next  5-minute  period  50  of  78  wasps  went  first  to  the  false 
entrance  and  afterward  found  the  true,  but  after  4  hours  only  15  out  of 
125  were  deceived.  The  blue  paper  was  then  left  over  the  nest  for  48  hours, 
when  it  was  moved  a  foot  and  a  half  to  the  west  to  put  it  directly  in  the 
line  of  flight  and  its  place  taken  by  a  yellow  paper,  which  gave  a  more 
decided  contrast  than  the  blue  had  to  the  red.  In  the  first  7  minutes  270 
wasps  returned,  none  of  which  flew  straight  into  the  true  entrance,  al- 
though many  passed  directly  over  it;  all  hovered  first  over  the  false, 
many  of  them  going  in  and  some  going  in  and  out  seven  or  eight  times, 
so  closely  was  the  blue  color  associated  with  the  idea  of  the  nest.  Three 
minutes  later,  during  a  5-minute  period,  205  wasps  first  entered  the  false 
and  then  the  true  hole;  not  one  flew  straight  to  the  true,  though  6  hesi- 
tated over  it  and  then  entered  without  going  to  the  false.  An  hour  later 
184  went  into  the  false  hole  and  202  into  the  true  one,  but  after  2  hours 
more,  only  76  entered  the  false  hole  to  191  for  the  true  one,  while  5  hours 
later  still  only  5  out  of  49  visited  the  false  entrance.  The  next  morning  only 
an  occasional  wasp  entered  the  false  hole,  though  one  came  and  searched 
in  the  grass  after  the  blue  paper  was  finally  removed. 

A  similar  test  was  made  with  yellow  paper,  one  of  slightly  darker  color 
being  substituted  after  an  exposure  of  3  days.  During  the  first  period 
nearly  a  third  of  the  wasps  were  deceived,  but  during  the  4  succeeding 
ones  only  about  one-eighth  of  them,  while  2  hours  later  this  dropped  as 
low  as  one-twentieth.  The  original  paper  was  replaced  and  2  days  later 
it  was  moved  10  inches  to  the  south,  leaving  the  ground  about  the  nest 
exposed  after  it  had  been  covered  with  different  papers  for  16  days.  During 
the  first  5  minutes  not  one  flew  straight  to  the  hole,  but  of  the  130  that 
entered  the  false  hole  61  finally  found  the  true  one.  When  the  false  paper 
was  moved  2  feet  to  the  south,  107  entered  the  true  hole  and  103  the  false, 
but  when  the  opening  in  the  yellow  paper  was  put  6  inches  from  the  hole 
and  a  red  one  placed  over  the  latter,  three  or  four  times  as  many  entered 
the  true  hole  as  the  false  one.  Somewhat  similar  results  were  obtained 
when  green  paper  was  substituted  for  the  red,  the  mistakes  growing  fewer 
with  increasing  experience.  When  the  green  paper  blew  over  the  hole 
and  the  wasps  could  not  get  in,  at  least  100  gathered  and  many  settled 
in  the  false  hole.  The  green  paper  was  taken  away,  exposing  the  ground 
about  the  nest,  but  only  3  or  4  entered.    As  soon  as  it  was  replaced  with 


EARLY  EXPERIMENTS   OF   PLATEAU   AND   OTHERS. 


145 


the  hole  above  the  entrance,  they  swarmed  in  6  or  7  at  a  time  and  in  a 
moment  all  had  disappeared;  it  was  plainly  the  color  that  had  directed 
them. 

Response  of  wasps  to  odor. — In  studying  the  attractive  effect  of 
odor,  the  Peckhams  surrounded  the  nest  with  paper  saturated  with  oil 
of  peppermint  or  wintergreen.  When  the  latter  was  employed,  a  third 
to  a  fourth  of  the  wasps  noticed  the  odor,  as  shown  by  starting  back  and 
circling  about.  A  plate  of  maple  sirup  placed  6  inches  from  the  nest  re- 
ceived no  attention  from  the  wasps,  though  visited  by  many  ants  and  flies 
and  one  bumble-bee.  Fresh  warm  chicken  bones  were  wrapped  in  several 
thicknesses  of  gauze  of  the  same  color  as  the  paper  around  the  nest  and 
placed  4  inches  to  one  side  of  the  entrance,  while  a  control  bundle  without 
bones  was  put  on  the  other  side.  In  15  minutes  25  different  wasps  visited 
the  first  bundle,  some  working  over  it  for  a  minute  or  two,  but  none  went 
to  the  second.  This  test  was  twice  repeated  with  the  same  results;  in  the 
last  case  3  wasps  worked  on  the  bundle  with  bones  for  15  minutes  and  then 
had  to  be  driven  away.  When  the  bones  were  cold,  fewer  wasps  noticed 
them  and  only  2  alighted,  and  2  days  later  after  they  had  become  dry  and 
relatively  inodorous,  but  2  out  of  129  wasps  landed  on  them.  A  dead  wasp, 
hidden  completely  in  the  grass,  attracted  5  others,  one  of  which  carried  it 
away.  Three  or  four  others  afterward  visited  the  spot,  probably  attracted  by 
the  scent  of  blood.  At  another  time  2  were  killed  and  the  ground  smoothed 
over  after  they  had  been  thrown  away;  in  15  minutes  9  wasps  came  to 
the  spot.  It  was  concluded  that  wasps  have  a  strong  sense  of  smell,  but 
that  they  pay  little  attention  to  odors,  however  powerful,  that  do  not 
indicate  food. 

MAIN  RESEARCHES  OF  PLATEAU. 
Masked  flowers. — In  the  first  paper  of  the  main  series  (1895:466), 
Plateau  set  himself  the  task  of  evaluating  the  attractive  power  of  color 
and  odor  by  masking  simple  heads  of  Dahlia  with  colored  paper  or  green 
leaves.  The  dahlias  grew  in  a  garden  with  petunias,  stocks,  nasturtiums, 
morning-glories,  zinnias,  phlox,  marigolds,  etc.,  all  of  which  were  being 
visited  by  species  of  Bombus,  Megachile,  Vanessa,  and  Pieris.  In  the  pre- 
liminary experiments  the  ray-flowers  were  covered  with  squares  of  paper, 
red,  violet,  white,  and  black  in  color,  the  yellow  disk  projecting  through  a 
hole  in  the  center.  During  an  hour  the  4  masked  heads,  which  were  on 
different  plants,  received  visits  as  follows: 


Table  89. 


Red. 

Violet. 

White. 

Black. 

Total. 

2 
8 
1 

0 
6 
0 

9 
3 
0 

0 

1 
0 

11 

18 

1 

Total 

11 

6 

12 

1                  30 

146 


PRINCIPLES  AND  CONCLUSIONS. 


While  the  heads  with  red  and  white  squares  seemed  to  be  much  more 
attractive,  this  was  shown  not  to  be  wholly  true  by  the  next  test,  in  which 
the  application  of  white  or  green  disks  to  the  center  of  the  heads  resulted 
in  masking  the  latter  entirely.  In  spite  of  this,  a  total  of  29  visits  was  re- 
corded, of  which  the  black  square  with  white  disk  received  7.  However, 
the  red  square  with  white  disk  still  yielded  the  largest  number,  and  a  direct 
comparison  between  black  and  white  was  lacking,  as  no  white  square 
was  employed  in  this  series.  Similar  results  were  obtained  with  a  disk 
masking  the  tubular  flowers  alone,  and  with  a  central  cylinder  and  a  black 
square. 

In  order  to  avoid  objections  arising  from  the  use  of  paper,  the  latter 
was  replaced  by  leaflets  of  Ampelopsis  in  the  remaining  experiments. 
When  the  rays  of  20  heads  much  sought  by  insects  and  well  distributed 
among  normal  heads  were  covered  with  leaflets,  with  only  the  yellow  disk 
in  evidence,  36  visits  were  noted  in  an  hour,  18  by  Bombus,  11  by  Vanessa, 
and  7  by  Megachile.  To  determine  whether  the  yellow  disk  still  furnished 
the  necessary  attraction,  this  was  effectively  concealed  in  each  of  the  20 
heads  by  a  smaller  leaflet.  In  spite  of  this  an  hour  period  yielded  58  visits, 
of  which  28  were  made  by  Bombus,  6  by  Vanessa,  5  by  Pieris,  and  1  by 
Megachile.  The  following  day  the  small  leaflet  was  placed  in  contact  with 
the  disk-flowers  in  16  heads  and  these  were  disposed  among  a  larger  number 
of  normal  heads.  Of  the  30  visits  made,  Bombus  afforded  19,  of  which  13 
were  successful  and  6  in  vain,  while  the  butterflies  made  6  unsuccessful 
to  3  successful  ones.  In  the  fourth  series  37  heads  were  completely  covered 
with  leaflets  and  the  remaining  ones  were  removed.  In  an  hour's  time  70 
visits  were  recorded,  distributed  as  follows. 


Total. 

Suc- 
cessful. 

Unsuc- 
cessful. 

36 
21 
13 

29 
10 

2 

7 
11 
11 

Total 

70 

41 

29 

The  author  contended  that  the  experiments  of  Bert,  Lubbock,  and 
others  gave  misleading  results,  since  it  was  impossible  to  give  two  dif- 
ferent colors  the  same  absolute  intensity.  This  conclusion  was  derived 
from  the  researches  of  Graber  (1884),  who  found  that  leucophile,  i.  e., 
light-seeking,  invertebrates  preferred  the  more  refrangible  rays,  while  the 
leucophobe  chose  the  less  refrangible,  red  producing  to  them  the  effect 
of  obscurity.  He  also  cited  the  observations  of  Forel  (1887)  and  others  to 
the  effect  that  the  sense  of  smell  is  much  better  developed  among  insects 
than  in  man,  and  that  the  perception  of  odors  is  very  different.  From  these 
facts  he  reached  the  conclusion  that  nothing  in  our  present  knowledge 
proves  that  insects  distinguish  colors  as  the  human  eye  does,  and  also  that 
they  perceive  odors  that  can  not  be  recognized  by  the  olfactory  nerve 
of  man.     His  final  conclusions  were  as  follows: 


MAIN    RESEARCHES    OF   PLATEAU.  147 

(1)  Insects  visit  actively  heads  in  which  form  and  color  are  masked  by  green  leaves. 

(2)  Neither  the  form  nor  bright  colors  of  flower  heads  seem  to  possess  attractive  power. 

(3)  The  colored  ray-flowers  of  simple  dahlias,  and  in  consequence  those  of  other 

radiate  composites,  do  not  have  the  vexillary,  or  signal,  role  attributed 
to  them. 

(4)  Since  form  and  color  appear  to  have  no  attractive  role,  insects  are  evidently  guided 

to  composite  heads  by  another  sense  than  sight.     This  is  probably  the 
sense  of  smell. 

Removal  of  corolla. — Plateau  removed  the  corolla  or  ray-flowers  in 
several  species  in  order  to  determine  the  role  in  attraction  (1896:505) 
The  first  experiment  was  made  with  Lobelia  erinus,  with  which  Darwin  had 
already  made  a  test  of  this  response  (1876:420).  The  latter  cut  off  all  the 
petals  of  certain  flowers  and  only  the  lower  striated  lip  of  others  and  found 
that  not  a  single  honey-bee  visited  them,  although  bees  were  abundant  on  the 
normal  flowers.  The  removal  of  the  small  upper  lip  had  no  effect.  Plateau 
used  two  pots  of  this  species,  one  with  30  and  the  other  with  40  flowers. 
These  were  placed  near  groups  of  Dahlia,  Petunia,  and  Tagetes  in  order  to 
afford  a  wider  choice  to  visitors.  The  corollas  of  one  pot  were  cut  back  to  the 
tube,  and  the  behavior  recorded  for  three  different  periods  of  1  to  2  hours. 
The  total  number  of  visitors  to  the  whole  flowers  was  33  against  25  to  the 
mutilated  ones,  Eristalis  tenax  giving  much  the  largest  number,  while 
there  were  29  inspections  to  the  former  and  16  to  the  latter.  Thus,  while 
there  was  a  larger  number  of  visitors  to  the  normal  flowers,  it  was  pointed 
out  that  the  suppression  of  the  corolla  did  not  prevent  them,  as  in  Darwin's 
results.  In  the  case  of  Oenothera  biennis,  one  honey-bee  was  seen  to  take 
nectar  from  14  mutilated  flowers  in  succession,  and  other  individuals  made 
respectively  10,  3,  and  15  visits  to  them,  the  last  one  returning  to  flowers 
already  visited.  When  the  corolla  of  Ipomoea  purpurea  was  cut  back  to 
the  sepals,  Bombus  muscorum  visited  successively  5  mutilated  flowers,  and 
B.  terrestris  in  like  manner  2,  3,  and  5  respectively. 

Kurr  (1833:135)  removed  the  floral  envelopes  of  Delphinium  ajacis  and 
D.  consolida  and  found  that  the  flowers  produced  seeds,  a  fact  that  aston- 
ished Darwin  (1.  c).  Plateau  made  a  similar  test  with  D.  ajacis,  removing 
all  the  petaloid  parts  except  the  nectary,  but  the  only  visit  was  made  by  a 
bumble-bee.  In  the  next  test  only  part  of  the  flowers  of  a  spike  were 
mutilated;  B.  terrestris  visited  the  intact  flowers  and  two  of  the  mutilated 
ones.  The  mutilation  experiment  made  by  Bonnier  (1878:61)  with  Digi- 
talis purpurea  was  also  repeated,  5  out  of  19  clusters  having  the  corolla 
cut  back  to  a  tube  1  cm.  long,  and  the  plants  being  intermingled.  Anthid- 
ium  and  Bombus  made  12  and  1  visits  and  11  and  5  inspections  respectively 
of  the  mutilated  flowers.  With  3  mutilated  spikes  out  of  5,  4  individuals  of 
B.  terrestris  merely  inspected  the  cut  flowers,  while  2  visited  5  and  6  of  them 
respectively.  The  next  day  the  same  setting  was  visited  by  4  bumble-bees 
of  the  same  species,  the  first  going  only  to  intact  flowers,  the  second  merely 
inspecting  the  mutilated  ones,  the  third  visiting  6  of  the  latter  in  succession 
after  normal  ones,  and  the  last,  9  in  similar  manner.  Antirrhinum  majus 
was  mutilated  by  cutting  the  corolla  back  to  1  cm.  in  8  spikes  out  of  25. 
Of  5  bumble-bees  observed,  3  merely  whirled  about  the  cut  clusters,  while 
the  other  two  flew  near  them  and  then  left  for  the  entire  flowers.     The 


148  PRINCIPLES  AND  CONCLUSIONS. 

author  remarked  that  if  he  had  worked  only  with  Antirrhinum  he  would 
have  been  persuaded  of  the  attractive  role  of  the  corolla,  but  regarded  this 
difference  in  response  to  two  related  genera  to  be  due  to  the  fact  that  the 
cut  flowers  of  Digitalis  are  still  directed  downward,  while  in  the  snapdragon 
the  stub  is  erect  and  much  more  difficult  to  reach. 

One  experiment  was  carried  out  on  Centaurea  cyanus  to  determine  the 
value  of  the  sterile  marginal  flowers  of  the  head,  which  were  regarded  as 
attractive  parts  by  Mueller  and  others.  The  show  flowers  were  removed 
from  10  heads  scattered  among  many  normal  ones.  During  an  hour  and 
a  half,  1  honey-bee  visited  a  mutilated  head,  while  Megachile  revisited  them 
to  a  total  of  19  heads,  behaving  exactly  as  at  the  normal  ones,  and  pass- 
ing readily  from  one  kind  to  the  other.  Observations  of  Darwin,  Mueller, 
Bonnier,  and  Van  Tieghem  were  cited  to  show  that  insects  visit  flowers 
of  which  the  corolla  has  fallen,  while  Van  Tieghem  had  similar  results  with 
Nicotiana,  from  which  he  had  cut  the  upper  part  of  the  corolla.  The  con- 
clusion of  Errera  and  Gevaert  (1878:141)  that  bees  are  guided  by  the  odor 
of  the  nectar  was  extended  to  include  all  pollinating  insects  and  to  be  true 
even  when  there  were  no  normal  flowers  to  assist  in  the  attraction. 

The  effect  of  masking  flowers  was  further  tried  on  a  very  fragrant  Hera- 
cleum,  the  single  plant  available  being  several  kilometers  from  any  others 
and  thus  apparently  eliminating  the  possible  action  of  habit.  An  umbel 
was  covered  with  leaves  of  rhubarb,  but  in  spite  of  this  received  7  visits  in 
a  half-hour.  Several  umbels  were  brought  close  together  and  covered  with 
leaves  in  a  similar  fashion,  receiving  45  visits  during  the  period  of  obser- 
vation. The  evidence  furnished  by  this  umbellifer  was  in  entire  accord 
with  that  obtained  from  Dahlia  and  was  regarded  as  proving  that  the 
insects  were  guided  by  the  sense  of  smell. 

Response  to  different  colors. — In  connection  with  his  experiments  on 
color,  (1897:17),  Plateau  emphasized  the  importance  of  the  work  of  Graber 
(1884,1885).  In  the  case  of  the  honey-bee,  the  latter  found  that  the  choice 
of  color  depended  upon  the  degree  of  refrangibility.  When  the  bee  was 
given  a  choice  between  bright  red  and  deep  blue,  it  went  to  the  latter, 
which  is  more  refrangible  though  less  luminous;  between  bright  red  and 
deep  yellow  it  chose  the  latter,  which  is  likewise  more  refrangible.  Be- 
tween dark  green  and  bright  yellow  it  exhibited  no  preference,  owing  to 
the  similar  refrangibility  of  the  two  colors,  in  spite  of  the  fact  that  the 
yellow  is  more  luminous.  In  consequence,  Plateau  concluded  that  insects 
do  not  see  color  as  such  at  all,  in  the  way  that  we  do,  but  that  they  respond 
to  the  different  ones  merely  in  relation  to  differences  in  refrangibility.  His 
observations  as  to  choice  of  color  were  made  upon  several  species  with 
flowers  of  various  colors.  In  the  case  of  Centaurea  cyanus  he  grew  blue, 
rose,  white,  and  dark-purple  varieties  in  mixture.  Both  Apis  and  Mega- 
chile were  observed  to  pass  readily  from  one  color  to  another,  though  22 
of  the  30  visits  were  to  blue  or  purple,  and  this  was  explained  by  the  greater 
number  of  the  blue  heads.  Unfortunately,  the  number  of  each  kind  was 
not  counted,  and  no  endeavor  was  made  to  arrange  the  installation  so  that 
the  number  of  each  would  be  the  same.  With  Dahlia  variabilis  the  colors 
were  scarlet,  purple,  rose,  salmon,  and  white,  among  which  the  visiting 


MAIN   RESEARCHES   OF   PLATEAU.  149 

bees,  butterflies,  and  syrphids  showed  not  the  least  choice,  though  no 
figures  were  given.  During  one  period  of  observation  pollinators  went  more 
frequently  to  purple  heads  of  Scabiosa  purpurea  and  during  another  to  the 
rose  ones,  the  explanation  being  that  this  was  due  to  the  greater  number 
of  heads  in  each  case.  Observations  by  Darwin,  Bonnier,  and  Errera  and 
Gevaert  were  also  cited  in  confirmation  of  these  results,  and  the  conclusion 
was  reached  that,  contrary  to  the  general  view,  insects  exhibit  the  utmost 
indifference  to  the  diverse  colors  to  be  found  in  the  same  species  or  the  same 
genus. 

Addition  of  honey  to  vivid  nectarless  flowers. — In  the  same  paper  were 
reported  the  results  of  experiments  made  upon  showy  flowers  with  little 
or  no  nectar,  in  confirmation  of  the  views  of  Darwin,  Bonnier,  and  Pe'rez, 
who  had  found  that  nectar  brought  visitors  in  abundance.  The  flowers  of  a 
border  of  Pelargonium  zonale  were  observed  to  be  completely  disdained  by 
Apis  and  Bombus.  A  drop  of  honey  direct  from  the  hive  was  placed  in  each 
flower  of  17  umbels  on  plants  arranged  in  a  continuous  series  and  marked  to 
prevent  confusion  with  normal  ones.  Bombus  terrestris  made  8  visits  in  an 
hour  to  the  honeyed  flowers,  entirely  neglecting  the  neighboring  nasturtiums. 
After  sipping  at  several,  he  would  fly  toward  the  normal  flowers,  but  only 
to  inspect  them  without  alighting.  The  next  day  honey  was  taken  from 
these  flowers  by  3  A  pis,  5  Bombus,  and  3  Vespa,  as  well  as  several  Diptera, 
and  a  little  later  by  18,  5,  and  5  individuals  respectively  of  the  same  genera, 
but  no  further  visits  were  seen  for  the  normal  flowers.  Flowers  of  Phlox 
paniculata,  which  were  but  little  visited  by  diurnal  insects,  were  provided 
with  honey,  a  drop  being  placed  in  20  flowers  of  the  violet  and  white  varie- 
ties. The  latter,  being  in  the  shade  at  the  time,  received  no  visits,  while 
6  were  made  to  the  former  by  A  pis,  Pieris,  and  Vespa,  the  two  bees  also 
making  9  visits  during  the  next  period  to  both  colors.  Honey  was  placed 
on  6  out  of  29  white  flowers  of  Anemone  japonica,  which  were  ordinarily 
little  visited  except  by  Diptera.  During  the  hour  100  visits  were  made  to 
intact  flowers  and  94  to  those  with  honey,  making  an  average  of  4.5  for  each 
of  the  former  and  15.6  for  the  latter.  A  single  flower  of  Convolvulus  sepium, 
which  had  been  completely  neglected,  received  29  visits  after  being  supplied 
with  honey,  though  few  of  these  were  made  by  bees. 

The  effect  of  removing  the  supply  of  nectar  was  determined  in  Dahlia  by 
excising  the  disk-flowers  of  8  heads  and  replacing  them  by  a  small  disk  cut 
from  a  yellowed  leaf  of  cherry.  No  insect  alighted  on  the  mutilated  heads, 
though  Bombus  and  Megachile  inspected  them  frequently.  This  behavior 
determined,  the  disks  were  coated  with  honey  and  the  visitors  immediately 
returned,  Bombus  making  26  visits,  Vespa  12,  and  Megachile  2  during  a 
half-hour.  Two  days  later  the  artificial  disks  were  dry  and  the  mutilated 
heads  were  again  entirely  neglected.  The  disks  were  removed  and  a  little 
honey  placed  in  the  greenish  cup  of  the  receptacle,  when  visitors  came  in 
abundance.  The  summary  stated  that  insects  go  without  hesitation  to 
flowers  habitually  neglected  by  reason  of  the  absence  or  paucity  of  nectar, 
when  they  are  supplied  with  artificial  nectar  in  the  form  of  honey.  They 
cease  their  visits,  even  in  the  presence  of  the  showy  ray-flowers,  when  the 
nectariferous  part  is  removed,  and  begin  them  again  when  honey  is  added. 


150  PRINCIPLES  AND  CONCLUSIONS. 

Anemophilous  flowers. — In  his  study  of  the  attraction  of  anemophi- 
lous  flowers  (1897:601),  Plateau  enumerated  Chenopodium  album,  Rumex 
obtusifolius,  Corylus  avellana,  Carex,  Anthoxanthum,  Agrostis,  Poa,  Festuca, 
Bromus,  Brachypodium,  and  Secale  as  already  known  to  be  visited  by  insects 
for  their  pollen,  and  cited  also  a  number  of  cases  in  which  extrafloral  nec- 
taries and  fruits  were  visited  by  bees  and  butterflies.  His  own  experiments 
were  carried  out  on  green  or  brownish  flowers  belonging  to  the  Chenopo- 
diaceae,  Urticaceae,  Polygonaceae,  Typhaceae,  Juncaceae,  Cyperaceae, 
and  Poaceae,  to  which  honey  was  added.  The  great  majority  of  the  visitors 
were  Diptera,  which  usually  came  within  a  few  minutes,  while  the  bees 
appeared  much  later.  It  is  perhaps  significant  that  Apis  went  to  12  of  the 
17  species,  the  wasps  Odynerus  and  Vespa  to  but  4,  and  Bombus  to  but  1. 
Rheum  tataricum,  which  combines  the  two  methods  of  pollination  to  some 
degree,  gave  somewhat  similar  results  with  honey,  but  Apis  was  entirely 
absent  and  2  species  of  Bombus  made  one  visit  each. 

Entomophilous  flowers  of  dull  color. — After  citing  the  frequent 
neglect  of  such  flowers  by  Darwin  and  Mueller,  and  the  emphasis  upon 
their  significance  by  Bonnier  and  MacLeod,  Plateau  (1897:613)  gave  a 
complete  summary  of  his  own  and  other  observations  upon  flowers  of  this 
type,  grouped  as  green,  greenish,  brown,  or  brownish.  In  the  first  group 
he  listed  43  species  belonging  to  18  families,  frequented  chiefly  by  Diptera, 
especially  the  muscids;  8  species  were  visited  by  Apis,  4  by  Bombus,  and  8 
by  other  bees,  usually  the  same  ones.  In  the  group  with  greenish  flowers  or 
inflorescences  were  placed  38  species  belonging  to  20  families,  of  which  10 
were  visited  by  A  pis,  4  by  Bombus,  and  6  by  other  bees,  the  vast  majority 
of  visitors  being  flies.  The  flowers  with  brown  or  brownish  color  numbered 
12  and  were  distributed  in  9  families,  6  of  the  species  being  visited  by  honey- 
bees. 

In  the  matter  of  anemophilous  flowers  the  conclusion  was  reached  that 
it  was  only  necessary  to  add  honey  in  order  to  attract  insects  in  large 
numbers.  Moreover,  insect  visits  were  abundant  to  91  species  of  ento- 
mophilous plants  that  lack  striking  color  in  the  corolla.  In  short,  insects 
concern  themselves  little  with  the  presence  or  the  absence  of  bright  floral 
parts;  what  they  desire  is  pollen  or  nectar.  They  are  guided  to  these  in 
a  very  secondary  degree  by  sight,  but  on  the  contrary  in  a  sure  manner 
by  another  sense,  which  can  only  be  that  of  smell. 

Artificial  flowers,  second  series. — The  first  experiments  of  Plateau, 
made  by  means  of  artificial  flowers  in  1876,  were  augmented  20  years  later 
by  studies  with  the  flowers  of  8  different  families  (1897:847).  In  all  cases 
the  flowers  were  copied  with  the  utmost  fidelity,  even  to  the  details  of 
stamens,  calyx,  etc.  With  Ribes  sanguineum  10  clusters  of  artificial  flowers 
were  placed  among  normal  ones,  but  of  5  individuals  of  Bombus,  3  of  Apis, 
and  3  of  Osmia,  not  one  was  seen  to  pay  the  slightest  attention  to  them. 
Two  branches  of  artificial  flowers  of  the  peach  were  suspended  among  the 
natural  ones  and  observed  for  three  different  periods  two  days  apart.  The 
bees  showed  complete  disdain  for  the  imitation  flowers,  even  when  they 
were  supplied  with  a  drop  of  honey,  as  on  the  last  day.  With  flowers  of  the 
cherry  the  results  were  the  same,  bumble-bees  and  honey-bees  both  passing 


MAIN  RESEARCHES  OF  PLATEAU.  151 

them  without  the  slightest  notice.  Similar  results  were  obtained  with  the 
apple,  except  that  the  flowers  with  a  drop  of  honey  were  visited  by  one 
wasp  and  many  flies.  No  visitors  came  to  the  artificial  flowers  of  Myosotis 
alpestris,  even  with  the  addition  of  honey,  while  with  those  of  Saxifraga 
umbrosa  2  individuals  of  Apis  and  1  of  Andrena  gave  them  a  hurried  in- 
spection. 

A  more  comprehensive  study  was  made  of  Digitalis  purpurea,  in  which 
the  habit  of  the  inflorescence,  the  form  of  the  corolla,  its  color,  and  markings 
were  copied  from  nature  with  great  care.  Among  6  natural  spikes  were  dis- 
posed 3  artificial  ones,  on  one  of  which  honey  was  placed  in  the  flowers.  On 
its  two  visits  Megachile  paid  no  attention  to  the  false  flowers,  while  4  of  10 
individuals  of  Bombus  inspected  them,  1  repeating  this  three  times.  In  the 
second  experiment,  3  natural  spikes  were  interspersed  with  3  false  ones,  1 
of  which  was  provided  with  honey.  Anthidium  ignored  the  artificial  flowers 
on  38  visits,  but  inspected  them  briefly  during  11  others,  while  one  Oxybelus 
actually  entered  a  false  corolla  containing  honey,  as  did  one  Odynerus  also. 
In  the  next  test,  made  when  the  natural  flowers  were  few,  Megachile  again 
ignored  the  false  flowers,  Anthidium  inspected  them  on  9  visits  out  of  31,  and 
two  individuals  of  Musca  alighted,  but  without  entering  the  corolla.  To 
eliminate  the  competition  of  the  natural  flowers  of  Digitalis,  3  clusters  of 
artificial  ones  were  placed  at  a  distance,  but  among  Dianthus  and  Tagetes. 
Of  the  many  visitors  to  the  latter,  but  3  individuals  inspected  the  false 
flowers  for  an  instant.  To  check  this  behavior  an  old  trunk  of  a  conifer, 
a  few  feet  in  height,  was  placed  in  the  spot  occupied  before  by  the  imitation 
clusters,  with  the  result  that  3  different  insects  were  observed  to  inspect 
it  on  two  different  occasions,  indicating  the  precautions  that  must  be  taken 
in  interpreting  mere  inspections. 

Three  clusters  of  false  flowers  were  suspended  in  a  mass  of  normal  ones 
of  Lathyrus  latifolius,  the  mimicry  being  so  close  that  it  would  not  have  been 
suspected  by  one  not  forewarned.  One  individual  of  Stelis  and  one  of  Bombus 
gave  an  instant's  attention  to  an  artificial  cluster,  while  Megachile  inspected 
it  in  10  of  17  visits.  To  test  the  significance  of  this,  3  pieces  of  pole  were 
placed  where  artificial  clusters  had  been,  when  it  was  found  that  Megachile 
made  9  inspections  of  them  in  the  course  of  36  visits.  When  the  imitation 
clusters  were  placed  4  dm.  in  front  of  the  main  group,  Bombus  ignored  them 
and  Odynerus  merely  alighted  for  a  moment  on  one  of  the  artificial  leaves. 
In  50  visits  Megachile  hovered  above  the  false  flowers  in  but  8  cases,  paying 
no  attention  whatever  to  them  in  the  others. 

Artificial  flowers  of  green  leaves. — To  avoid  the  objection  arising  from 
the  use  of  something  other  than  vegetable  tissue  and  to  further  test  the 
response  to  green  objects  furnished  with  honey,  leaves  of  Ribes  rubrum  and 
Acer  pseudoplatanus  were  rolled  into  cups,  the  free  edges  trimmed,  and 
honey  placed  in  the  center.  Six  flowers  of  this  type  were  attached  to  several 
branches  of  Symphoricarpus  racemosus,  where  they  were  almost  invisible 
in  the  mass  of  foliage.  In  a  half-hour  the  leaf  flowers  had  received  19  visits, 
chiefly  from  flies;  the  bees  were  represented  by  two  visits  of  Apis.  In  the 
next  test  Apis  made  8  visits,  1  more  than  by  the  other  insects,  and  in  the 
third,  Bombus  furnished  2  of  the  15  visits,  again  chiefly  due  to  flies.     The 


152  PRINCIPLES  AND  CONCLUSIONS. 

bumble-bees  attempted  to  pierce  the  leaf  with  their  mandibles,  but  desisted 
after  several  minutes,  as  the  thickness  was  too  great.  Finally,  two  leaf 
flowers  were  fastened  to  the  peduncles  of  simple  heads  of  Dahlia,  the  one 
made  from  the  leaf  of  maple  being  erect,  the  other  from  the  currant, 
hanging.  The  first  received  14  visits,  of  which  5  were  by  Bombus,  and  the 
second  but  4  visits,  none  of  them  from  bees. 

Incidentally,  Plateau  made  a  series  of  tests  with  various  essences,  such 
as  lavender,  sage,  thyme,  mint,  etc.,  but  found  that  they  exerted  little 
attraction.  Thyme  and  sage  alone  afforded  a  feeble  attraction,  while  the 
effect  of  mint  was  to  repel  the  insects. 

Conclusions  as  to  artificial  flowers. — From  the  above  results,  Plateau 
came  to  the  following  conclusions : 

(1)  In  general,  the  insects  observed  paid  no  attention  to  artificial  flowers  of  bright 

color,  whether  empty  or  provided  with  honey;  they  even  seemed  to  avoid  them. 

(2)  In  the  few  cases  where  they  seemed  to  notice  the  presence  of  the  artificial  flowers, 

they  merely  hovered  about  them,  a  behavior  also  exhibited  before  other  bodies 
without  any  resemblance  to  flowers. 

(3)  The  insects  did  not  attempt  to  enter  the  flowers  made  of  paper  or  cloth,  even  when 

furnished  with  honey. 

(4)  On  the  contrary,  the  leaf  corollas,  marked  by  the  natural  plant  odor,  and  normal 

green  color,  and  provided  with  honey,  received  numerous  visits. 

(5)  The  attractive  influence  of  bright  artificial  colors  can  consequently  be  regarded 

as  practically  null. 

General  summary. — In  completing  the  series  of  five  papers  on  the  way 
in  which  flowers  attract  insects,  Plateau  enunciated  the  following  prin- 
ciples. 

Insects  seeking  pollen  or  nectar  are  guided  to  the  flowers  that  contain 
these  substances  in  only  a  subordinate  degree  by  sight.     In  fact: 

(1)  Neither  the  form  nor  the  bright  colors  of  flowers  seem  to  have  an  important 

attractive  role. 

(2)  Insects  visit  actively  the  heads  of  composites  and  the  umbels  of  umbellifers  not 

mutilated  but  with  the  forms  and  colors  masked  by  green  leaves. 

(3)  Insects  continue  to  visit  flowers  or  inflorescences  in  which  practically  all  the  bright- 

colored  organs  are  removed,  such  as  petals,  corolla,  disk-flowers,  etc. 

(4)  They  exhibit  neither  preference  nor  antipathy  for  the  different  colors  afforded 

by  the  flowers  of  different  varieties  of  the  same  species  or  of  related  species, 
passing  from  a  white  flower  to  a  blue  one,  then  to  purple,  rose,  etc.,  without 
appreciable  choice. 

(5)  Insects  easily  discover  and  actively  visit  numerous  green  or  greenish  flowers, 

which  are  but  slightly  visible  in  the  midst  of  the  leaves. 

(6)  They  ordinarily  pay  no  attention  to  artificial  flowers  of  paper  or  cloth,  even  though 

brightly  colored  and  well-executed,  and  provided  with  honey.  They  even  seem 
to  avoid  them. 

(7)  On  the  contrary,  artificial  corollas  made  of  green  leaves  receive  numerous  visits 

when  provided  with  honey. 

Insects  are  guided  in  an  accurate  manner  to  flowers  with  pollen  or  nectar 
by  some  other  sense  than  vision  and  this  can  only  be  the  sense  of  smell : 

(1)  They  go  without  hesitation  to  those  flowers  habitually  neglected  because  of  the 
lack  or  paucity  of  nectar,  just  as  soon  as  one  provides  them  with  an  artificial 
nectar  in  the  form  of  honey. 


MAIN  RESEARCHES  OF  PLATEAU.  153 

(2)  Insects  cease  their  visits  when,  without  disturbing  the  bright-colored  parts,  one 

removes  the  nectar-bearing  part  of  the  flower,  and  they  begin  them  again  if 
the  missing  nectar  is  replaced  by  honey. 

(3)  It  is  sufficient  to  put  honey  in  or  upon  inconspicuous  green  or  brownish  anemoph- 

ilous  flowers  rarely  visited,  to  attract  numerous  insects. 

(4)  The  r61e  of  the  sense  of  smell  is  also  demonstrated  by  leaf  flowers  filled  with  honey. 

Role  of  vexillary  organs. — The  attractive  value  of  colored  bracts 
and  show-flowers  furnished  the  theme  of  the  first  investigation  in  a  new 
series  of  studies  on  the  relations  between  insects  and  flowers,  begun  by 
Plateau  in  1897  (1898:339).  The  vexillary  role  of  the  terminal  group  of 
vivid  bracts  of  Salvia  horminum  was  first  studied,  making  use  of  a  bed  of  this 
species  more  than  a  square  meter  in  extent.  This  resembled  a  rose  carpet 
as  seen  from  above,  while  the  flowers  themselves  were  hardly  visible,  except 
at  the  edge.  The  numerous  bees  present,  chiefly  Apis  and  Anthidium, 
went  directly  to  the  flowers  upon  their  arrival,  noticing  the  colored  bracts 
only  as  they  flew  upward  from  flower  to  flower  or  when  the  folded  bracts 
simulated  the  flowers.  The  butterflies  were  more  easily  deceived,  1 
Pieris  and  3  Rhodocera  landing  on  the  bracts  and  trying  to  probe  them  with 
the  proboscis.  Six  honey-bees  were  observed  to  make  but  one  visit  and  one 
inspection  of  the  bracts  to  388  visits  to  the  flowers.  In  order  to  eliminate 
the  possibility  that  this  behavior  was  due  to  habit  arising  from  the  fact 
that  Salvia  had  been  grown  for  several  years  in  the  same  spot,  plants  were 
transferred  to  another  garden  more  than  2  km.  distant,  where  they  were 
placed  in  a  circle  within  another  of  Dianthus  barbatus.  Thus,  the  visiting 
insects  were  offered  three  choices,  between  the  flowers  of  Dianthus,  those  of 
Salvia,  and  the  bracts  of  the  latter,  the  last  two  being  presumably  new  to 
them.  The  insects  that  hovered  without  landing  on  either  Dianthus  or 
Salvia  were  106  in  number,  all  butterflies  or  moths,  with  the  exception  of  3 
individuals  of  Bombus.  During  the  period,  26  individuals  of  bees,  49 
butterflies,  48  flies,  and  16  beetles  visited  Dianthus  alone,  without  paying 
any  attention  to  Salvia.  Of  21  individuals  that  visited  Dianthus  and  were 
also  confused  by  Salvia,  all  were  Lepidoptera,  with  the  exception  of  one 
Andrena.  Three  out  of  6  individuals  of  Macroglossa  hovered  over  the 
colored  bracts  of  Salvia,  one  making  this  mistake  3  times.  In  the  case  of 
the  insects  visiting  Salvia  alone,  the  bees  observed  numbered  250,  but  only 
24  of  these  made  even  a  slight  mistake,  while  there  was  on  an  average  one 
error  for  each  butterfly  and  each  fly. 

With  reference  to  the  attraction  exerted  by  show-flowers,  Plateau  em- 
ployed two  species  of  Hydrangea,  the  one  native  and  with  a  clear  distinction 
between  the  small  fertile  flowers  of  the  center  of  the  umbel  and  the  large 
sterile  ones  of  the  margin,  the  other  cultivated  and  exhibiting  umbels  with 
large  sterile  flowers  alone.  The  number  of  visitors  to  the  native  species 
was  small,  a  few  bees  and  syrphids  coming  for  pollen  alone.  The  behavior 
of  these  was  characteristic,  for,  instead  of  alighting  first  on  the  large  mar- 
ginal flowers  as  demanded  by  the  theory  of  their  attractive  rdle,  they  flew 
by  or  above  them  as  though  they  did  not  exist,  in  order  to  land  directly  on 
the  fertile  central  ones.  The  number  of  mistakes  made  was  but  1  for  the 
bees  out  of  79  visits,  while  for  the  less  intelligent  flies  it  was  1  for  18  umbels 
visited.    In  the  case  of  the  cultivated  species  neither  the  brilliance  of  the 


154  PRINCIPLES  AND  CONCLUSIONS. 

umbels  nor  their  large  number  served  to  attract  honey-bees,  bumble-bees, 
or  butterflies,  except  for  rare  visits  or  inspections.  The  sole  visitors  were 
Syrphus  and  Melanostoma,  which  went  almost  exclusively  to  the  flowers 
with  stamens.  The  total  number  of  errors  for  the  bees  was  5  in  397,  for  the 
flies  5  in  93.  The  author  dismissed  the  possibility  that  this  was  due  to 
habit,  partly  because  of  the  short  life  of  the  individuals  and  partly  because 
of  the  way  he  assumed  this  would  affect  the  numbers  found  on  the  umbels. 
He  regarded  these  results  as  proving  conclusively  that  the  vexillary  organs 
studied  actually  attracted  the  majority  of  insects  so  little  and  the  higher 
bees  to  such  a  minimum  degree  that  the  fertilization  of  these  species  would 
in  no  wise  suffer  by  their  absence,  and  that  they  could  no  longer  be  consid- 
ered as  organs  of  attraction. 

Choice  of  colors  by  insects. — The  first  half  of  this  second  paper  of  the 
series  (1899:336)  is  devoted  to  a  critical  resume"  of  experiments  by  others 
made  by  means  of  colored  objects  and  by  means  of  natural  intact  flowers, 
together  with  an  account  of  desirable  and  undesirable  methods  to  be  em- 
ployed in  such  studies.  The  first  experiments  were  made  with  the  two 
varieties  of  Salvia  horminum,  one  of  which  had  pale-rose  flowers  and  bright- 
rose  bracts,  while  the  other  possessed  violet-blue  flowers  and  deep-blue 
bracts.  These  grew  in  contiguous  beds  and  were  trimmed  back  to  give  the 
same  dimensions  to  the  two  groups.  The  observations  were  made  during 
an  hour  each  day  for  12  days,  a  representative  record  giving  125  visits  to 
rose  and  131  to  blue,  with  5  abrupt  changes  from  rose  to  blue  and  7  from 
blue  to  rose.  The  addition  of  the  numbers  series  by  series  gave  the  predom- 
inance alternately  to  rose  and  blue,  the  final  totals  being  1,085  rose  and 
847  blue,  and  this  was  regarded  as  explaining  the  preference  obtained  by 
Lubbock  for  blue  and  Bennett  for  rose.  The  equality  of  the  two  colors 
was  further  shown  by  the  fact  that  Anthidium  and  Megachile  flew  suddenly 
from  rose  to  blue  in  64  cases  and  from  blue  to  rose  in  75,  while  one  individual 
of  the  former  visited  first  5  blue,  then  2  rose,  4  blue,  4  rose,  1  blue,  and  4  rose. 

For  a  number  of  insects  and  flowers  the  percentages  of  each  color  and 
of  the  visits  were  computed  and  the  results  expressed  in  table  90. 

In  further  experiments  it  was  found  that  the  honey-bee  went  to  scarlet 
without  the  least  repugnance.  Pieris  brassicae  eagerly  visited  the  red 
and  yellow  heads  of  Zinnia,  while  the  related  Goniopteryx  seemed  to  neglect 
these  colors.  One  individual  of  Pieris  visited  indifferently  the  red,  rose,  and 
yellow  heads  of  Zinnia,  but  another  went  only  to  rose  heads  of  Scabiosa. 

In  his  conclusions,  Plateau  emphasized  the  fact  that  he  had  at  no  time 
said  that  insects  did  not  see  the  colors  of  flowers.  He  affirmed,  however, 
that  we  have  no  practical  means  of  assuring  ourselves  that  they  perceive 
colors  and  that  this  perception  is  the  same  as  with  man.  The  results  of  all 
experiments  made  with  colored  papers,  cloths,  or  glass,  or  with  isolated  petals 
or  normal  flowers  can  be  explained  either  by  differences  in  the  amount  of 
light  reflected,  or  by  differences  in  the  refrangibility  of  the  rays  transmitted 
or  reflected.  Whatever  may  be  the  visual  perception  of  insects,  the 
question  whether  the  insects  that  visit  flowers  are  guided  in  their  choice  by 
the  colors  that  flowers  present  to  the  human  eye  must  be  answered  in  the 
negative.     In  studying  the  response  of  insects  to  varieties  of  the  same 


MAIN  RESEARCHES  OF  PLATEAU. 


155 


species,  which  eliminates  the  effect  of  differences  of  form,  perfume,  and 
the  abundance  and  accessibility  of  nectar  or  pollen,  it  has  been  seen  that 
they  show  a  complete  indifference  to  color,  when  the  relative  number  of  the 
flowers  of  each  color  available  is  taken  into  account.  Finally,  it  was  ad- 
mitted that  insects  perceive  flowers  from  a  distance,  either  because  they 
see  colors  as  we  do  or  because  they  perceive  a  certain  contrast  between 
the  flowers  and  their  surroundings,  and  that  concurrently  with  the  sense 
of  smell,  although  to  a  considerably  smaller  degree,  this  visual  perception 
can  direct  them  toward  the  mass  of  flowers.  Once  arrived  there,  however, 
if  the  flowers  differ  from  each  other  in  color  alone,  they  are  perfectly  indif- 
ferent whether  the  corollas  are  blue,  red,  yellow,  white,  or  green. 

Table  90. — Color  preferences. 


Species. 

Color. 

No.  of 
flowers. 

No.  of 
visits. 

White 

p.  ct. 

60.9 
39.0 
55.2 

44.7 

p.  ct. 
60.1 
39.8 
49.1 
50.8 

Bom  bus  terrestris :  Delphinium  ajacis 

Blue 

Color. 

Heads. 

Visits. 

Bombus  terrestris :  Scabiosa  atropurpurea. . . 

p.  ct. 

56.4 

33.8 

9.6 

69.6 

12.9 

8.9 

8.4 

70.6 

18.6 

10.6 

27.8 

54.0 

18.0 

p.ct. 
52.6 
42.1 

5.2 
76.4 
13.5 

7.3 

2.7 
75.0 
21.8 

3.1 
25.0 
42.8 
32.0 

White 

Blue 

Violet 

White 

Yellow 

Wrhite 

Red 

Yellow 

Errors  made  by  Anthidium. — Plateau  (18992:452)  concluded  that 
the  female  of  Anthidium  manicatum  was  directed  to  the  flowers  of  Salvia 
horminum  by  the  odor,  since  these  were  much  smaller  and  much  less  con- 
spicuous than  the  group  of  terminal  bracts.  In  following  her  behavior  it 
is  seen  that  she  makes  many  mistakes ;  she  often  returns  to  a  flower  already 
visited,  goes  to  partly  faded  flowers  with  the  upper  lip  brownish,  and  even 
to  completely  faded  ones  which  fall  with  her,  and  finally  alights  uselessly 
upon  the  buds.  The  male  is  frequently  unable  to  see  the  female  when  the 
latter  is  immobile,  but  perceives  her  instantly  when  she  flies.  Moreover, 
he  is  often  unable  to  recognize  the  same  individual  again,  sometimes  return- 
ing to  her  twice.  So  much  does  he  depend  upon  movement  that  more  than 
once  he  was  seen  to  fly  to  females  of  other  genera  even,  such  as  Megachile, 
Anthophora,  Apis,  and  an  ichneumon  fly.     However,  he  did  not  disturb 


156  PRINCIPLES  AND  CONCLUSIONS. 

females  of  Pieris,  recognizing  them  as  different  by  their  staccato  flight  and 
large  white  surface.  It  was  concluded  that  the  observations  given  for  this 
one  species,  belonging  apparently  to  those  better  endowed  mentally,  show 
how  necessary  it  is  to  distrust  statements  as  to  the  perfect  clearness  of  the 
vision  of  Hymenoptera. 

Admiration  of  syrphids  for  bright  flowers. — In  the  third  and  last 
paper  of  this  series  (1900:266),  Plateau  discussed  the  current  views  as  to 
the  admiration  exhibited  by  syrphids  for  bright-colored  flowers.  To  refute 
this  view  he  listed  35  species  with  green  or  greenish  flowers  for  which  charac- 
teristic visits  by  syrphids  were  recorded,  and  gave  a  large  number  of  obser- 
vations in  which  species  of  Syrphus  in  particular  hovered  in  the  usual 
fashion  over  leaves  and  other  objects.  In  addition,  he  showed  by  experi- 
ment that  these  flies  could  be  made  to  respond  as  usual  by  means  of  a 
variety  of  objects,  such  as  a  finger,  the  tip  of  a  cane,  etc.,  His  conclusions 
were  as  follows: 

(1)  The  number  of  cases  clearly  described  of  supposed  shows  of  admiration  for  the 

color  of  flowers  is  very  limited  and  may  be  reduced  to  seven  altogether  out  of  the 
thousand  described  by  naturalists. 

(2)  The  only  insects  noted  are  the  dipterous  syrphids,  with  limited  faculties  inferior 

to  those  of  the  bees. 

(3)  The  syrphids  regularly  exhibit  their  so-called  admiration  before  flowers  not  only 

without  bright  colors,  but  also  before  green  and  greenish  ones. 

(4)  They  frequently  hover  before  other  plant  parts  than  flowers,  such  as  green  leaves, 

green  buds,  and  fruits,  green  and  brown  stems. 

(5)  Syrphids  also  exhibit  their  characteristic  stationary  flight  before  objects  having 

no  resemblance  to  flowers,  such  as  a  finger,  a  cane,  a  marble,  or  a  string. 

(6)  As  a  consequence,  admiration  for  the  color  of  flowers  does  not  exist  among  insects. 

Attraction  of  colored  cloths  and  brilliant  objects. — Plateau  em- 
ployed banner-like  pieces  of  colored  cloth  to  determine  the  attraction  of 
color  when  not  associated  with  flowers  (19002: 174).  In  the  first  experiment 
the  colors  used  were  bright  red,  yellow,  bright  violet,  and  sky-blue,  the 
cloths  being  suspended  on  leafy  branches  at  about  a  meter  above  the  soil. 
The  sole  response  to  the  banners  was  made  by  a  single  individual  each  of 
Musca,  Calliphora,  and  Megachile,  which  seemed  to  rest  on  the  yellow  cloth 
as  on  any  object.  However,  7  individuals  of  Eristalis  and  1  honey-bee 
hovered  over  a  fringe  of  blue  wool.  The  position  of  the  colors  was  then 
changed,  but  the  results  were  similiar;  Pieris  was  attracted  slightly  by  the 
blue,  one  Eristalis  and  Bombus  rested  on  the  violet  piece,  while  11  Eristalis, 
4  Syrphus,  and  1  Pieris  hovered  over  the  blue  fringe.  Two  further  tests 
were  made  with  much  the  same  results,  the  entire  series  yielding  30  cases 
of  probable  and  8  of  doubtful  attraction.  All  but  2  of  the  first  were  caused 
by  the  blue  fringe,  as  well  as  4  of  the  latter.  Of  the  total,  5  visits  were  made 
by  bees,  29  by  flies,  chiefly  syrphids,  and  4  by  buttei flies. 

To  determine  the  effect  of  brilliant  objects,  four  spheres  of  metallic 
luster  and  4  to  6  cm.  in  diameter  were  employed.  One  of  these  was  red 
above  and  blue  below,  the  second  had  these  colors  reversed,  while  the  other 
two  were  glass  silvered  within.  These  were  suspended  on  stakes  at  the 
usual  height  of  the  flowers  visited.  All  told,  there  were  24  cases  of  evident 
attraction  and  10  doubtful  ones,  the  silvered  spheres  furnishing  14  of  the 


MAIN  RESEARCHES  OF  PLATEAU.  157 

former.  The  bees  comprised  19  of  the  evident  attractions,  of  which  Apis 
and  Bombus  each  made  4  to  the  silvered  spheres,  and  Bombus  7  to  the 
colored  ones. 

Plateau  repeated  the  experiment  of  PeVez,  who  found  that  insects  were 
attracted  to  pieces  of  colored  cloth  when  these  were  hung  among  masked 
flowers.  Pieces  of  the  colored  cloths  and  the  blue  fringe  previously  used 
were  hung  among  13  masked  heads  of  Dahlia  and  3  of  Rudbeckia  and  at  the 
same  level.  The  visiting  insects  paid  practically  no  attention  to  the  shreds 
of  cloth,  in  spite  of  the  fact  that  they  hovered  over  both  buds  and  fruits.  One 
honey-bee  and  2  Eristalis  inspected  the  blue  fringe,  and  two  of  the  latter 
and  one  Lucilia  alighted  for  a  moment  on  the  yellow  piece. 

In  general,  brightly  colored  pieces  of  cloth  attracted  so  few  insects  that 
it  is  impossible  to  deduce  from  this  an  argument  in  favor  of  the  attraction 
of  insects  by  the  colors  of  flowers.  Pieces  of  colored  cloth  suspended  near 
flowers  masked  with  leaves  attracted  no  more  insects  than  when  they  were 
placed  near  normal  flowers.  Brilliant  objects  with  metallic  luster  seemed 
to  exercise  a  slightly  greater  attraction  than  colored  cloth.  From  this 
it  may  be  concluded  that  the  attraction  produced  by  certain  objects  other 
than  flowers  is  probably  related  to  the  amount  of  light  reflected.  In  certain 
flowers  supposed  to  be  without  odor,  such  as  Dahlia  for  example,  a  real  odor 
can  be  disclosed  by  a  simple  process. 

Constancy  among  bees. — After  citing  the  observations  of  Bennett, 
Christy,  Bulman,  and  Ord  on  the  constancy  shown  by  insects  as  to  the 
flower  visits  made  during  each  flight;  from  the  nest  or  hive  (1901:56), 
Plateau  gave'the  results  obtained  from  his  own  studies.  A  tabular  expo- 
sition was  made"  of  the  visits  of  42  individuals  belonging  to  4  species  of 
Bombus,  in  which  the  bee  flew  from  one  species  to  another  and  in  13  in- 
stances to  a  third,  showing  complete  indifference  to  structure  and  color. 
In  contrast  to  Bombus,  Anthidium  was  found  to  be  very  constant,  and  it 
was  only  with  difficulty  that  8  cases  of  inconstancy  were  observed,  two  of 
them  comprising  3  species.  As  shown  by  the  results  of  earlier  investiga- 
tors, the  honey-bee  proved  also  very  constant,  though  not  completely  so. 
In  three  successive  summers  Plateau  found  only  14  instances  of  incon- 
stancy, and  but  2  of  these  concerned  a  third  species. 

None  of  the  apids  observed  exhibited  an  absolute  constancy.  Bombus 
was  much  the  most  inconstant,  rarely  remaining  faithful  even  for  a  short 
time  to  the  same  species.  Anthidium  and  Apis  presented  a  remarkable 
fidelity,  which,  however,  suffered  certain  clear  exceptions.  In  all  the  cases 
observed,  the  bees  passed  from  the  flowers  of  a  certain  species  and  color 
to  those  of  other  species,  often  of  a  different  color  and  family,  thus  giving 
proof  of  a  complete  indifference  to  flower  structure  and  coloration.  The 
acquisition  of  pollen  and  nectar  is  their  sole  motive. 

Mistakes  made  by  bees. — Plateau  recorded  in  detail  the  mistakes 
made  by  7  species  of  Hymenoptera  in  visiting  37  species  of  flowers  belonging 
to  19  different  families.  The  time  involved  was  rather  more  than  6  hours 
scattered  through  22  days.    The  results  are  given  in  table  91. 

It  was  concluded  that  probably  no  pollinating  hymenopter  is  exempt 
from  error  and  that  the  honey-bee  is  deceived  as  frequently  as  others. 


158 


PRINCIPLES  AND  CONCLUSIONS. 


Table  91. 


Species. 


No.  of 
individuals. 


No.  of 
errors. 


Proportion  per 
individual. 


Apis  mellifica 

Bom  bus  hortorum 

muscorum 

lapidarius 

Megachile  centuncularius 

ericetorum 

Odynerus  quadratus 

Total 


107 


186 


1.8 
1.5 
2.2 
1.0 
1.0 
1.0 
1.0 


Removal  of  the  antennae  of  bumble-bees. — In  the  introduction  to 
this  paper  (19022:414),  Plateau  stated  that  up  to  that  time  he  had  attributed 
a  secondary  role  to  sight  and  a  preponderant  one  to  smell,  and  likewise 
called  attention  to  the  results  of  many  investigators,  including  Forel  and 
himself,  who  had  shown  that  with  the  insects  the  sense  of  smell  resides 
chiefly  if  not  exclusively  in  the  antennae.  Forel  (1901:53)  cut  the  antennas 
of  6  individuals  of  Bombus  at  the  base  and  set  the  bees  free  again.  At  the 
end  of  5  minutes  a  male  returned  to  visit  8  to  10  flowers  of  Convolvulus 
in  succession,  each  time  flying  directly  to  the  flower  without  a  second's 
hesitation.  He  was  caught  to  confirm  the  complete  absence  of  the  antennae 
and  then  released,  when  he  made  a  single  turn  in  the  air  and  came  back 
at  once  to  the  flowers  to  visit  them  as  before.  At  the  same  time,  several 
of  the  bumble-bees  deprived  of  their  antennae  returned  to  the  bindweed 
flowers,  flying  from  one  to  the  other  with  even  more  precision  if  possible 
than  those  with  the  antennae  intact.  Two  days  later  several  males  and 
small  females  with  the  antennae  cut  were  found  flying  from  flower  to  flower 
with  an  astonishing  rapidity  and  precision. 

Plateau  repeated  the  experiments  of  Forel  on  two  occasions.  In  1899 
the  antennae  were  cut  from  10  individuals  of  Bombus  terrestris  and  1  ot  B. 
muscorum,  on  four  nearly  successive  days.  These  at  once  flew  away,  but 
one  returned  the  first  day  to  the  same  flowers,  and  on  the  following  days, 
and  in  3  cases  shortly  after  the  operation,  6  bees  without  antennae  were 
captured,  including  the  B.  muscorum.  Although  more  than  half  of  the 
multilated  bees  had  found  their  way  back  to  the  flowers,  the  experiment 
was  repeated  in  1902  to  remove  certain  doubts,  especially  with  respect  to 
the  thoroughness  with  which  the  antennae  were  removed.  The  latter  were 
consequently  cut  at  the  level  of  the  head  and  the  bees  released.  The  results 
were  as  follows:  4  neuters  of  B.  terrestis  never  returned;  of  11  B.  hortorum, 
10  females  and  1  neuter,  only  1  female  returned;  1  male  and  1  female  came 
back  out  of  7  individuals  of  B.  lapidarius;  finally,  of  8  B.  hypnorum,  5  re- 
turned shortly  after  the  operation.  Thus,  8  bumble-bees  out  of  30  returned 
accurately  to  the  preferred  species  of  flower  after  the  antennae  had  been 
completely  removed  and  guidance  by  smell  was  impossible. 


MAIN  RESEARCHES  OF  PLATEAU.  159 

Evidence  of  the  attractive  role  of  odor. — Plateau  properly  insisted 
that  the  above  results  did  not  indicate  that  the  sense  of  smell  played  no 
part  in  attraction,  and  he  brought  forward  a  number  of  facts  to  prove  this 
and  in  particular  the  investigations  of  Mayor  and  Gorka. 

(1)  Flowers  that  seem  to  man  to  have  no  odor  may  be  shown  to  possess  it  by  the 

proper  method,  and  these  would  be  perceived  by  insects  with  the  sense  of  smell 
well  developed. 

(2)  Many  champions  of  the  importance  of  the  corolla  in  attraction  have  adznitted  that 

in  certain  cases  odor  can  attract  insects  more  strongly  than  color. 

(3)  The  apids  are  much  more  attracted  by  odor  than  is  ordinarily  believed.     Honey- 

bees and  bumble-bees  seek  actively  the  extrafloral  nectar  of  stipules,  petioles, 
and  leaves,  while  the  former,  with  many  flies  and  wasps,  visit  fallen  and  dry 
fruits. 

(4)  The  olfactory  sense  of  many  insects  is  extraordinary  and  guides  them  from  con- 

siderable distances  to  objects  that  frequently  they  can  not  see,  as  in  the  case  of 
saprophilous  flies  and  beetles.  Wasps  readily  find  such  desired  food  as  cooked 
meat,  and,  like  bees,  are  often  attracted  in  great  numbers  to  fruits,  preserves, 
etc.  Numerous  observations  have  been  made  of  the  attraction  from  the  fields 
of  male  moths  by  a  captive  female  inclosed  in  a  room  or  in  a  box. 

(5)  Moths  are  captured  at  night  by  means  of  perfumed  sugar  solutions  placed  on 

tree  trunks,  cords,  apples,  etc. 

Mayor  (1900)  clearly  demonstrated  the  unique  importance  of  the  sense 
of  smell  in  connection  with  the  sex  attraction  in  Callosamia  promethea. 
Males  of  this  species  when  released  more  than  30  meters  from  a  glass  vase 
covered  with  mosquito  netting  and  containing  5  females,  flew  directly  to 
the  vase  and  hovered  about  the  opening.  When  the  vase  was  inverted  in 
sand  so  that  the  females  could  be  seen  but  no  emanation  could  escape,  the 
males  flew  away,  only  to  return  when  the  vase  was  placed  again  in  the 
original  position.  When  the  female  was  wrapped  up  in  loose  cotton,  the 
males  flew  to  the  latter  and  gathered  on  it.  After  the  females  were  inclosed 
in  a  box  with  a  paper  chimney  at  one  end  and  a  lattice  at  the  other,  the  males 
flew  to  the  opening  of  the  former,  through  which  the  odor  was  drawn.  When 
the  abdomens  of  the  females  were  detached  and  placed  on  a  table  and  the 
winged  thorax  placed  near  by,  the  males  went  only  to  the  former.  If  the 
antennae  of  the  male  were  covered  with  varnish,  glue,  paraffin,  or  other  sub- 
stances capable  of  excluding  the  odor,  it  no  longer  sought  the  female  or 
even  noticed  it  at  a  distance  of  a  few  centimeters.  Plateau  pointed  out  that 
the  experiments  of  Gorka  (1900:57)  seemed  to  demonstrate  that  odor 
should  be  taken  into  account  as  well  as  sight,  since  the  individuals  of  Deili- 
phila  with  the  eyes  covered  with  black  varnish  immediately  found  the 
flowers  of  Borrago  and  Malta,  and  shortly  afterward,  the  preferred  ones  of 
Phlox.  He  further  stated  that,  if  he  had  been  incorrect  in  assigning  an 
exaggerated  importance  to  smell,  his  many  observations  and  experiments 
proved,  as  Knuth  had  admitted,  that  the  sense  of  smell  played  a  much 
more  important  role  in  the  attraction  of  insects  by  flowers  than  had  been  ad- 
mitted up  to  that  time. 

Decorollate  poppies  and  insect  visits. — In  repeating  Giltay's  experi- 
ments with  flowers  of  Papaver  from  which  the  petals  had  been  removed 
(p.  171),  Plateau  pointed  out  two  errors  in  the  method  that  he  regarded 


160  PRINCIPLES  AND  CONCLUSIONS. 

as  serious  (19023:657).  In  order  to  remove  the  petals  before  the  flowers 
were  visited  by  insects,  Giltay  excised  them  before  the  corolla  expanded, 
which  led  to  the  flowers  being  handled  for  too  long  a  time.  He  also  paid  no 
attention  to  the  behavior  of  the  insects  on  the  mutilated  and  on  the  intact 
flowers.  Hence,  Plateau  took  precautions  to  work  on  Papaver  orientate, 
a  species  more  abundantly  visited  and  easier  to  observe  than  P.  rhoeas, 
to  remove  the  petals  with  the  minimum  of  disturbance,  and  to  observe  the 
number  and  behavior  of  the  insects  in  minute  detail.  In  addition  some 
buds  were  enclosed  in  netting  and  the  stems  tied  to  stakes  to  prevent  the 
access  of  insects  and  the  transfer  of  pollen  in  consequence  of  being  shaken 
by  the  wind.  During  a  typical  period  there  were  1  fresh  and  18  old  de- 
corollate  and  13  normal  flowers  under  observation.  The  single  fresh  muti- 
lated flower  received  20  visits,  of  which  17  were  made  by  Apis  and  3  by  Halic- 
tus. During  this  time  the  13  normal  flowers  yielded  56  visits,  or  an  average 
of  4.3  to  20  for  the  mutilated  one.  While  frequent  visits  were  made  to  old 
decorollate  flowers,  these  were  always  brief,  the  insect  quickly  recognizing 
its  error.  The  total  number  of  visits  to  30  multilated  flowers  was  137,  Apis 
making  97  and  Halictus  19,  while  70  normal  flowers  received  172  visits, 
of  which  Apis  contributed  121  and  Halictus  18.  The  former  received  an 
average  of  4.5,  the  latter  of  2.4  visits.  As  to  the  weight  of  seed,  the  70 
capsules  of  the  intact  flowers  produced  21.07  gm.,  and  those  of  the  mutilated 
ones  6.5  gm.;  the  respective  averages  per  capsule  were  0.30  and  0.21  gm., 
giving  a  ratio  of  1:1.39  in  favor  of  the  normal  flowers.  In  the  matter  of 
germination  no  difference  was  found  between  the  two  kinds  of  flowers. 

In  conclusion,  the  removal  of  the  petals  reduced  the  number  of  seeds 
per  flower,  as  Giltay  had  shown.  This  result  probably  did  not  come  from 
the  removal  of  the  attractive  corolla,  since  the  mutilated  flowers  received 
as  many  or  even  more  visits  than  the  normal  ones.  It  was  really  due  to  the 
different  behavior  of  the  insects  on  the  two  flowers  in  their  quest  for  pollen. 
They  hang  from  the  stamens  of  the  decorollate  flowers  and  pull  them  below 
the  ovary,  with  the  consequence  that  they  neither  carry  pollen  to  the  stigmas 
nor  shake  any  upon  it.  On  the  contrary,  in  the  normal  flower  they  pass 
between  the  corolla  and  the  crown  of  stamens,  which  they  shake  vigorously 
by  the  movements ;  they  also  wander  over  the  stigmatic  disk.  As  a  conse- 
quence, the  mutilated  flower  is  reduced  to  the  less  effective  autogamy,  while 
the  normal  benefits  by  the  action  of  allogamy. 

New  experiments  with  artificial  flowers. — In  reply  to  a  number  of  his 
critics,  Plateau  performed  a  much  more  comprehensive  series  of  tests  with 
artificial  flowers  in  1904  and  1905,  in  the  course  of  which  he  made  66  experi- 
ments of  an  hour's  duration  with  10  different  genera,  5  of  which  were 
composites  (19062:3).  His  criticisms  of  the  methods  of  Andreae,  Reeker, 
Wery,  and  others  are  considered  later  under  the  authors  concerned,  and  the 
present  account  is  restricted  to  his  own  investigations  and  the  consequent 
conclusions.  In  making  the  artificial  flowers  especial  pains  were  taken  to 
avoid  the  use  of  any  attractive  material  whatsoever,  as  well  as  to  copy  the 
flower  faithfully  as  to  habit,  size,  and  color.  Translucid  colored  papers  of 
the  usual  kind  were  employed  alone  for  the  flowers  of  thinner  texture,  while 
for  others  the  paper  was  first  pasted  upon  tarlatan  cloth,  but  without  alter- 


MAIN  RESEARCHES  OF  PLATEAU.  161 

ing  the  transparence.  For  an  adhesive,  pure  gum  arabic  alone  was  used, 
since  it  never  attracts  insects,  and  for  stuffed  parts,  only  cork,  wadding,  or 
tow.  Paste  anthers  were  avoided  and  all  delicate  parts,  such  as  disk  flowers, 
were  made  of  paper  cut  into  a  fringe.  At  the  time  of  each  experiment,  all 
artificial  flowers  were  provided  with  natural  foliage. 

When  21  artificial  flowers  of  Crocus,  10  yellow  and  11  white,  were  placed 
in  a  bed  of  normal  flowers  of  C.  luteus  and  vernus,  they  received  but  one 
visit,  that  of  a  muscid,  and  two  inspections  from  Osmia,  in  the  course  of 
three  experimental  periods,  in  spite  of  abundant,  visits  to  the  normal  flowers. 
In  the  case  of  Viola  odorata,  the  imitations  received  two  visits  from  Vanessa 
and  11  inspections  from  Osmia  in  47  visits,  while  Apis  ignored  them  entirely. 
Paper  flowers  of  Althea  rosea  were  provided  in  one  series  with  stamens  of 
commerce,  afterwards  found  to  contain  much  starch  and  some  dextrin- 
like substance,  while  in  the  second  series,  fringed  paper  was  employed  for 
the  stamens  to  avoid  the  possibility  of  attraction  by  the  starch.  Two  art- 
ificial stems  with  6  white  and  7  rose  flowers  were  attached  to  2  out  of  4 
plants  with  the  buds  still  closed.  Eight  insects  landed  on  the  imitation 
flowers,  7  merely  inspected  them,  and  15  ignored  them.  When  the  arti- 
ficial clusters  were  placed  near  natural  ones  the  latter  yielded  55  visits 
to  3  inspections  of  the  former  in  one  case  and  50  visits  to  but  4  inspections 
in  the  other.  In  the  experiment  given  from  the  second  series  an  artificial 
cluster  of  6  flowers  was  placed  4  meters  in  front  of  natural  ones  bearing 
20  flowers.  One  Apis  and  Bombus  and  5  Prosopis  inspected  the  false  clusters. 

Three  cloth  flowers  of  Papaver  orientalis  were  arranged  among  unopened 
buds,  but  out  of  45  insects,  only  3  individuals  of  Pieris  inspected  them. 
When  placed  in  competition  with  a  bed  of  Myosotis  alpestris,  3  such  flowers 
secured  no  attention  from  the  honey-bee.  A  mixture  of  4  normal  flowers 
with  3  artificial  ones  yielded  51  visits  to  the  former  and  1  visit  and  4  in- 
spections by  Apis  to  the  latter,  while  in  the  five  experiments  there  were 
but  10  inspections  or  visits  to  the  artificial  flowers  as  compared  with  198 
visits  to  normal  ones.  Six  artificial  heads  of  Scabiosa  atropurpurea  were 
placed  at  the  edge  of  a  cluster  containing  more  than  60  natural  heads, 
receiving  4  inspections  to  53  visits  to  the  latter.  When  the  imitations 
were  placed  a  meter  in  front  of  the  cluster,  they  received  5  inspections 
to  36  visits.  When  imitation  heads  of  Dahlia  variabilis  were  attached 
at  the  proper  level  to  stalks  not  yet  in  bloom,  4  individuals  of  Apis,  1  of 
Megachile,  4  small  bees,  2  muscids,  and  1  Lucilia  inspected  them,  out  of 
the  host  of  insects  in  the  garden.  The  9  artificial  heads  were  next  fastened 
on  stalks  bearing  3  normal  heads  in  full  bloom,  with  the  result  that  28 
insects  visited  the  latter  directly  and  10  passed  near  the  imitations  without 
noticing  them.  Twelve  insects  went  directly  to  the  latter  and  3  visited 
them  after  a  normal  head,  all  of  these  merely  making  an  inspection,  with 
the  exception  of  3  butterflies.  The  same  9  imitations  were  placed  2  meters 
before  8  plants  bearing  18  heads,  and  the  number  of  inspections  was  con- 
siderably decreased,  namely,  to  4  out  of  51,  as  would  be  expected  from 
the  distance  between  the  two  groups. 

The  effect  of  grouping  on  the  response  to  artificial  flowers  was  especially 
well  shown  by  the  experiments  with  Zinnia  elegans.  When  20  imitations 
were  placed  3  meters  from  a  plot  of  this  plant,  they  received  2  inspections 


162  PRINCIPLES  AND  CONCLUSIONS. 

and  11  visits,  at  2  meters  1  inspection  and  9  visits,  while  the  mixture 
of  artificial  and  natural  heads  yielded  23  visits.  When  2  imitation  heads 
of  Helianthus  annuus  were  placed  on  stems  with  closed  buds,  they  received 
2  inspections  by  Bombus  and  13  incidental  visits  from  muscids  chiefly, 
while  33  insects  ignored  them  entirely.  The  number  of  inspections  was 
increased  when  the  2  imitations  were  placed  among   15  normal  heads, 

9  insects  coming  to  inspect  and  2  to  alight,  among  them  being  Apis  and 
Bombus.  With  3  normal  and  2  artificial  heads,  27  insects  ignored  the  latter 
as  they  flew  past,  and  5  inspected  them.  In  order  to  test  the  attraction 
exerted  by  the  materials  used  in  ordinary  artificial  flowers,  a  head  bought 
in  a  store  was  added  to  the  two  previously  used.   The  result  was  that  the 

10  inspections  observed  either  took  place  before  this  one  head  or  began 
with  it,  indicating  that  the  starch  or  dye  employed  in  it  served  as  the 
attraction.  Twelve  heads  of  Leucanthemum  vulgare  bought  in  the  trade 
were  attached  to  a  plant  bearing  1  open  head  and  25  to  30  buds,  but  re- 
ceived a  single  incidental  visit  and  no  inspections.  The  next  experiment 
was  organized  by  placing  5  imitations  among  30  open  heads  of  the  same 
plant  and  putting  a  group  of  7  artificial  heads  at  a  distance  of  a  meter. 
No  visits  were  made  to  the  latter,  in  contrast  to  3  to  those  on  the  plant 
and  53  to  the  normal  ones,  thus  indicating  that  the  natural  flowers  furnished 
the  attraction  for  the  others. 

The  most  comprehensive  series  of  experiments  was  made  with  Centaurea 
cyanus,  in  which  both  bought  and  specially  constructed  artificial  flowers 
were  employed.  Six  clusters  of  3  heads  each  of  the  former  were  attached 
to  plants  with  the  buds  still  closed,  which  grew  near  groups  of  Melandrium 
and  Anchusa  actively  visited  by  bees.  Apis  and  Bombus  inspected  the 
false  heads  30  times  and  extended  the  ligule  before  them  5  times.  When 
artificial  heads  made  for  the  purpose  were  employed,  Apis  made  1  inspection 
and  Bombus  5  only.  However,  these  were  made  a  year  later  and  under 
different  conditions  of  weather  and  competition.  The  author  admitted 
that  the  bees  frequenting  the  adjacent  flowers  gave  evident  attention 
to  the  imitation  heads,  but  stated  that  they  perceived  them  only  from  a 
short  distance,  attraction  from  a  distance  seeming  not  to  exist  or  to  be 
very  feeble  so  far  as  the  artificial  heads  were  concerned.  When  18  of  the 
commercial  flowers  were  put  at  2  dm.  from  a  group  of  normal  ones,  they 
obtained  15  inspections  and  2  extensions  of  the  ligule  in  comparison  with 
54  visits  to  the  latter,  while  the  special  imitations  when  placed  in  and 
about  a  nearly  equal  number  of  natural  heads  received  but  9  inspections. 
In  a  series  of  5  comparative  studies  with  both  kinds  of  artificial  heads 
the  figures  were  essentially  similar,  though  the  inspections  were  more  marked 
with  the  commercial  heads.  Altogether,  the  cornflowers  attracted  insects 
somewhat  more  than  the  other  artificial  flowers. 

Conclusions  as  to  artificial  flowers. — Because  of  their  value  in  sum- 
ming up  the  results  of  his  three  investigations  with  artificial  flowers  and  giving 
his  final  views  on  the  subject,  Plateau's  conclusions  are  here  stated  in  detail : 

"With  respect  to  the  solution  of  the  question  whether  insects  are  or  are  not  seriously 
attracted  by  artificial  flowers,  these  new  and  extensive  experimental  studies  are 
almost  useless,  since  they  serve  only  to  confirm  in  full  the  results  of  my  earlier  re- 


MAIN  RESEARCHES  OF  PLATEAU.  163 

searches.  They  confirm  these  all  the  more,  since,  advised  by  the  criticisms,  I  have 
endeavored  to  avoid  everything  that  could  lead  to  objections:  it  has  been  said  that 
the  imitations  employed  were  too  few  in  number  compared  with  the  normal  flowers; 
this  time  I  have  used  numerous  examples  and  in  several  cases  the  numbers  of  the  real 
flowers  and  of  the  copies  were  essentially  the  same;  it  has  been  objected  that  I  have 
not  tried  the  attraction  of  imitations  completely  isolated;  I  have  now  done  this  repeat- 
edly; the  erroneous  objection  has  been  made  that  my  artificial  flowers  have  been 
nothing  but  gross  imitations;  I  have  continued  to  use  only  the  most  careful  imitations 
possible  and  have  frequently  employed  the  very  same  species  utilized  by  my  critics. 

"I  can  then  only  repeat  the  conclusions  that  I  have  formulated  earlier,  modifying 
the  words  alone  a  little  in  order  to  avoid  all  ambiguity,  and  emphasizing  the  necessity 
of  good  experimental  conditions: 

"1.  In  much  the  greater  number  of  cases  insects  pay  no  attention  to  artificial  flowers 

of  vivid  color  and  frequently  treat  them  merely  as  obstacles  in  their  way. 
"2.  In  the  relatively  small  number  of  cases  where  they  perceive  the  presence  of  the 

imitations,  they  usually  show  only  a  brief  hesitation,  which  is  revealed  by  a 

turn  or  a  crochet  before  or  around  them. 
"3.  Insects  never  seek  pollen  or  attempt  to  suck  nectar  in  a  flower  truly  artificial  and 

containing  no  attractive  material  of  any  sort. 
"4.  The  attractive  influence  of  bright  artificial  colors  can  in  consequence  be  regarded 

as  nearly  null. 

"However,  if  this  laborious  study  has  ended  only  in  the  demonstration  of  the  accur- 
acy of  my  earlier  results,  it  has  permitted  what  is  perhaps  more  important,  the  dis- 
covery of  most  of  the  errors  committed  by  my  opponents  and  the  reasons  why  they 
have  believed  in  good  faith  in  the  actual  attraction  of  artificial  flowers.  Such  errors 
are  as  follows: 

"A.  To  cover,  conceal,  cut  or  suppress  in  any  manner  the  natural  flowers  and  to 
replace  them  with  artificial  ones.  In  this  case,  insects,  and  especially  the 
bees,  not  finding  pollen  or  nectar  where  it  was  on  former  visits,  fly  in  seeking 
it  about  any  object  occupying  the  place  or  located  near  it. 

"B.  To  place  artificial  flowers  near  or  among  natural  ones.  Under  such  conditions  it 
happens  occasionally .  that  insects  which  start  by  going  directly  to  the  real 
flowers,  in  passing  from  one  flower  to  another  or  in  leaving,  hesitate  before 
an  artificial  one  as  one  sees  them  stop  before  faded  flowers  or  even  closed  buds. 

"C.  To  make  studies  with  artificial  flowers  in  places  where  they  have  already  been 
performed  with  natural  ones,  since  such  places  might  have  become  habitually 
visited  by  bees,  for  example. 

"D.  Not  to  have  taken  into  account  the  significant  difference  between  a  direct  flight 
and  simple  turns  or  crochets  of  inspection. 

"E.  To  disregard  the  well-known  details  of  behavior,  thus  to  forget  that  syrphids 
may  hover  before  any  object  whatsoever,  that  the  muscids  alight  constantly 
upon  the  most  diverse  surfaces,  chiefly  to  expose  themselves  to  the  sun,  that 
Pieris  whirls  about  all  kinds  of  plants  and  projecting  objects,  that  small  Hymen- 
optera  such  as  Stelis  and  Prosopis  fly  about  and  land  upon  anything;  finally,  to 
take  for  visits  the  momentary  or  accidental  presence  upon  artificial  flowers  of 
carnivorous  insects  or  others  that  are  not  attracted  by  real  flowers. 

"F.  To  employ  the  artificial  flowers  of  commerce  or  those  made  by  florists.  Such 
imitations  may  contain  parts  taken  from  natural  flowers;  they  are  nearly 
always  impregnated  with  starch;  they  are  sometimes  dyed  with  chlorophyll  or 
other  plant  colors ;  the  stamens  and  pistils  are  always  represented  by  small  balls 
of  paste  more  or  less  attractive  to  certain  insects,  faults  whose  importance  I 
do  not  wish  to  exaggerate,  but  which  probably  explain  the  cases  noted  of  an 
apparent  search  for  pollen,  of  attempts  to  suck  pollen,  and  of  visits  to  the  flowers 
of  ladies'  hats." 


164  PRINCIPLES  AND  CONCLUSIONS. 

Macroglossa  and  false  flowers. — In  order  to  throw  light  upon  the 
numerous  observations  of  visits  by  Macroglossa  stellatarum  and  other  in- 
sects to  artificial  and  painted  flowers,  Plateau  (1906:141)  collected  all 
the  known  cases  of  this  sort,  commented  on  them  critically,  and  carried 
out  several  series  of  experiments  to  show  the  slight  value  pertaining  to  the 
observations.  The  significance  of  the  latter  and  of  Plateau's  objections 
is  discussed  later  (p.  189),  the  experiments  alone  being  taken  up  at  this 
point.  The  flight  of  Macroglossa  is  astonishingly  swift,  Bedel  noting  an 
average  of  50  flowers  of  jasmine  visited  per  minute,  and  Plateau  observ- 
ing 301  flowers  of  Phlox  paniculata  sought  in  succession.  In  the  experi- 
ments with  colored  cloths,  rectangles  of  silk,  wool,  etc.,  varying  in  size 
from  a  12mo.  to  a  4to.  page  and  ranging  from  red  through  yellow  to  blue, 
and  rose,  were  attached  to  four  stakes  placed  at  the  corners  of  a  large 
bed  of  Delphinium  ajacis.  The  7  experiments  with  varying  combinations 
gave  the  following  results:  (1)  the  12  hawk-moths  observed  always  flew 
directly  to  the  flowers,  never  to  the  cloths;  (2)  no  moth  paid  any  real 
attention  to  the  cloths,  two  only  making  a  rapid  exploratory  curve  about 
the  blue  woollen  fringe;  (3)  none  of  the  other  insects  noticed  the  colored 
cloths,  not  even  the  blue  fringe.  In  the  next  series,  the  objection  raised 
earlier  by  Perez  was  met  by  using  small  pieces  of  cloth  4  cm.  square,  which 
were  hung  near  the  flowers  of  Dianthus  and  Phlox.  In  no  case  did  the  hawk- 
moths  go  to  the  bits  of  cloth,  even  bounding  over  them  as  so  many  ob- 
stacles to  visiting  the  flower.  Similar  results  were  obtained  by  employing 
pieces  of  colored  paper,  14  by  10  cm.,  a  single  Macroglossa,  and  one  of  Papilio 
and  Bombus  merely  inspecting  the  papers.  When  screens  covered  with 
paper  on  which  bright  flowers  were  painted  were  employed,  no  hawk- 
moth  gave  them  the  slightest  attention,  and  this  was  true  of  a  large  number 
of  bees  and  butterflies.  Two  butterflies,  two  bees,  and  a  wasp  merely 
alighted  on  the  screen  for  a  moment's  repose,  as  shown  by  the  fact  that 
one  of  them  landed  on  the  unpainted  side,  while  one  Apis  and  one  Vespa 
flew  up  and  down  along  the  screen.  Four  experiments  were  made  with  a 
large  number  of  artificial  flowers,  which  permitted  the  study  of  the  behavior 
of  6  individuals  of  Macroglossa.  At  least  100  such  flowers  were  placed  in 
two  groups  near  a  mass  of  Anchusa,  and  at  a  distance  of  a  meter,  and  in 
the  second  experiment  they  were  scattered  in  and  about  a  border  of 
Dianthus.  While  99  flowers  of  Anchusa  and  110  of  Dianthus  were  visited 
by  hawk-moths,  no  notice  was  taken  of  the  imitations,  and  a  similar  result 
was  obtained  in  the  final  experiment. 

Plateau  refrained  from  giving  formal  conclusions  at  the  end  of  this 
paper,  partly  because  his  studies,  though  prolonged  and  laborious,  were 
rendered  incomplete  by  the  destruction  of  the  gardens  in  the  midst  of 
which  he  worked. 

"New  researches,  by  means  of  other  methods,  will  be  necessary  and  I  hope  there 
will  somewhere  be  found  a  serious  investigator  to  undertake  them,  rather  than  a  super- 
ficial observer  content  with  approximations.  I  have  conscientiously  endeavored  to 
deceive  Macroglossa  by  means  of  colored  paper,  large  and  small  pieces  of  cloth,  flowers 
painted  upon  wall-paper,  artificial  flowers,  and  the  colored  bracts  of  Salvia  horminum. 


MAIN  RESEARCHES  OF  PLATEAU.  165 

It  is  possible,  it  is  even  probable  that  several  of  my  experiments  have  been  defective ; 
I  believe,  however,  that  it  is  impossible  that  all  of  these  observations  and  experiments, 
made  during  five  successive  summers,  are  absolutely  bad.  A  single  consideration 
diminishes  my  regret  at  not  being  able  to  carry  them  further,  namely,  that  the  present 
work  contains  a  number  of  documents  which  it  will  be  neceessary  to  take  into  account  in 
writing  the  history  of  Macroglossa  stellatarum." 

Entomophilous  flowers  little  visited  by  insects. — The  final  memoir 
by  Plateau  (1910:3)  was  devoted  to  experiments  with  entomophilous  flow- 
ers with  bright  colors  but  without  nectar.  The  investigations  were  made 
in  the  spring  and  summer  of  1907,  1908,  and  1909,  and  comprised  55  ex- 
periments upon  a  dozen  species.  The  substances  employed  to  render  the 
flowers  attractive  were  anisette,  composed  of  very  dilute  alcohol,  sugar 
sirup,  and  a  small  amount  of  essence  of  anise,  brown-sugar  sirup  with  rum, 
sugary  juice  of  cooked  cherries,  and  sugar  sirup  with  a  decoction  of  An- 
gelica. The  first  two  species  employed  were  Fumaria  officinalis  and  Poly- 
gonum convolvulus,  both  with  very  small  inconspicuous  flowers.  When 
anisette  was  placed  upon  these  by  means  of  a  brush,  insects  were  immedi- 
ately attracted  to  them,  the  visitors  being  chiefly  flies.  The  experiments 
dealt  chiefly  with  large  flowers  of  a  vivid  color,  which  are  normally  little 
or  not  at  all  visited  by  insects.  When  Lilium  candidum  was  supplied  with 
anisette  or  brown-sugar  sirup,  visitors  appeared  almost  at  once,  the  total 
number  reaching  28  in  an  hour,  of  which  25  were  honey-bees.  As  a  check, 
flowers  were  supplied  with  sirup  alone,  but  these  were  visited  by  only  a 
small  number  of  flies,  no  bees  noticing  them.  A  single  flower  of  Passifiora 
with  the  corolla  moistened  with  anisette  received  34  visits  by  flies,  while 
another  was  supplied  with  brown-sugar  sirup  with  rum  a  few  days  later 
and  yielded  40  visits  in  an  hour,  of  which  1  was  by  Apis,  2  by  Bombus, 
and  several  by  Vespa.  Five  experiments  were  made  with  Oenothera  speci- 
osa,  the  first  one  with  anisette  showing  visits  by  Halictus  and  Prosopis 
chiefly,  while  the  second,  on  the  afternoon  of  the  same  day,  yielded  20 
visits,  19  by  Apis  and  1  by  Prosopis.  Similarly  treated,  Pisum  sativum 
received  30  visits,  chiefly  of  Bombus  and  Megachile,  and  Linum  perenne, 
15  visits,  11  of  which  were  by  flies,  3  by  bees,  and  1  by  a  hawk-moth. 
The  juice  of  cooked  cherries  was  put  in  the  flowers  of  3  umbels  of  Pelar- 
gonium zonale  and  anisette  in  those  of  another  two.  While  the  natural  clusters 
were  not  visited  at  all,  those  treated  received  a  number  of  visitors,  practi- 
cally all  flies.  Clematis  jackmanni  perfumed  with  anisette  gave  20  visits 
in  an  hour,  of  which  14  were  made  by  Bombus,  and  Convolvulus  sepium 
received  numerous  visits  from  4  genera  of  Hymenoptera,  5  of  Diptera,  and 
1  of  Lepidoptera.  In  the  case  of  Petunia  hybrida  provided  with  cherry 
juice,  40  honey-bees  came  during  a  period  of  an  hour,  and  visits  continued 
actively  for  a  day  or  more,  even  to  flowers  completely  faded,  as  long  as 
the  juice  was  available.  In  the  second  experiment,  cherry  juice  was  placed 
in  the  flowers  of  a  group  situated  at  a  distance  of  5  meters  from  the  first 
one,  but  no  visits  occurred  for  more  than  4  hours,  and  the  number  then  was 
much  smaller  than  in  the  previous  case. 


166  PRINCIPLES  AND  CONCLUSIONS. 

The  results  of  this  series  of  experiments  were  summarized  in  the  fol- 
lowing conclusions: 

1.  These  observations  confirm  the  fact,  already  known  but  not  sufficiently  empha- 

sized, of  the  existence  of  a  considerable  number  of  entomophilous  flowers  of 
large  size  and  bright  color  that  attract  diurnal  insects  little  or  not  at  all. 

2.  Two  corollaries  may  be  derived  from  this  fact:  the  first  is  that  the  attractive  r61e 

of  the  form  and  color  of  the  floral  envelopes  is  either  null  or  nearly  so;  the 
second  is  that  other  causes  than  the  attraction  of  colored  surfaces  is  necessary 
to  bring  pollinators  to  flowers  and  to  cause  them  to  return,  such  as  an  odor  pleas- 
ing to  insects  and  a  sugary  liquid. 

3.  The  addition  of  these  two  attractions  to  nectarless  flowers  that  are  little  visited  has 

the  practically  certain  consequence  of  causing  insects  to  come  to  them,  fre- 
quently in  large  numbers. 

4.  This  type  of  experiment,  previously  made  by  means  of  honey,  succeeds  just  as 

well  when  sugar  sirup  perfumed  with  an  odor  properly  chosen  is  employed,  a 
fact  which  proves  that  the  criticisms  directed  against  the  use  of  honey  are 
not  well  founded. 

5.  To  obtain  good  results  it  is  necessary  to  avoid  the  use  of  most  of  the  pure  essences 

of  commerce  and  of  artificial  perfumes,  and  to  employ  substances  already  known 
to  attract  insects,  others  of  which  will  doubtless  be  discovered.  It  is  also 
necessary  to  work  on  clear  days  and  during  the  warmest  part  of  the  day,  as  well 
as  to  renew  the  solution  from  time  to  time  so  that  the  odor  will  continue  to 
attract. 

6.  The  immediate  or  nearly  immediate  arrival  of  insects,  not  only  flies  but  frequently 

bees  as  well,  at  flowers  thus  treated  demonstrates  clearly  the  olfactory  sensi- 
tiveness of  insects  and,  in  spite  of  all  the  objections  raised,  proves  the  import- 
ance of  the  role  of  smell  in  the  attraction  of  insects  by  flowers. 

7.  In  resume^  the  present  investigation  but  confirms  the  thesis  advanced  in  1S97  in  the 

following  words:  "Insects  seeking  pollen  or  nectar  are  guided  to  the  flowers 
that  contain  these  substances  in  only  a  subordinate  degree  by  sight.  They 
are  guided  in  an  assured  manner  to  such  flowers  by  some  sense  other  than 
vision,  and  this  can  only  be  the  sense  of  smell." 

RELATED  STUDIES  AND  CRITIQUES. 
Comparative  importance  of  odor  and  color. — As  a  consequence  of 
Plateau's  first  paper,  P6rez  (1894:245)  brought  together  the  results  of 
a  number  of  observations  and  several  experiments  to  show  that  both  color 
and  odor  serve  for  attraction,  as  Lubbock  had  already  demonstrated. 
With  reference  to  the  attraction  of  red  flowers,  he  found  that  Salvia  splen- 
dens  was  not  visited  by  honey-bees  while  in  the  shade,  but  as  soon 
as  the  sun  reached  it  a  number  of  visitors  came  almost  immediately.  This 
was  explained  as  being  due  to  the  effect  of  the  sun's  rays  in  favoring  the 
excretion  of  nectar  or  freeing  its  perfume,  and  not  to  the  greater  visibility, 
but  the  latter  seems  much  more  probable.  When  honey  was  placed  on 
the  corolla  of  flowers  of  a  scarlet  Pelargonium,  honey-bees  working  on  neigh- 
boring heliotropes  were  at  once  attracted  by  its  odor  and  went  directly 
to  the  flowers,  which  they  continued  to  visit  until  evening.  They  even 
returned  in  the  morning,  although  the  honey  had  been  exhausted  the  eve- 
ning before,  when  they  also  went  to  flowers  that  had  not  received  honey 
and  examined  them  thoroughly.  Perez  concluded  that  at  a  distance  where 
vision  could  not  be  an  aid,  bees  and  the  great  majority  of  insects  are   di- 


RELATED  STUDIES  AND  CRITIQUES.  167 

rected  by  the  odors  carried  by  currents  of  air  and  thus  reach  the  flowers 
that  exhale  them.  As  soon  as  they  approach  sufficiently  near  for  sight 
to  intervene,  they  fly  directly  to  the  flowers  in  response  to  guidance  by 
vision.  Color  likewise  serves  to  attract,  in  the  absence  of  odor  previously 
perceived,  when  the  chances  of  the  flight  bring  them  near  a  flower.  They 
then  visit  the  latter  if  the  odor  is  pleasing,  or  disdain  the  flower  if  the  odor 
is  unpleasant. 

In  a  more  extensive  paper  (1903:1),  Perez  communicated  the  results  of 
further  experiments  and  discussed  at  some  length  the  points  of  difference 
between  Plateau  and  himself.  When  fallen  flowers  of  Glycine  were  inter- 
spersed with  bits  of  paper  of  the  same  color,  a  honey-bee  inspected  them, 
but  flew  away  before  landing,  to  seek  nectar  in  some  of  the  flowers.  Small 
balls  of  rose  paper  were  strung  on  a  pin,  which  was  fixed  on  the  end  of  a 
leafy  shoot  of  Symphoricarpus  or  on  a  shoot  from  which  the  flowers  had 
been  removed,  and  in  some  cases  all  the  open  flowers  of  a  cluster  were 
replaced  by  similar  balls  of  paper.  Two  honey-bees  inspected  the  paper- 
balls  for  a  moment,  while  a  bumble-bee  gave  them  more  extended 
attention.  When  the  rose  flowers  of  a  currant  were  hidden  by  means  of 
green  leaves  and  bits  of  cloth  of  the  same  color  placed  near  them,  several 
honey-bees  were  deceived  by  the  latter,  though  they  finally  found  the 
masked  clusters.  Similar  results  were  obtained  from  a  small  orange  tree 
ornamented  with  small  pieces  of  white  paper.  The  addition  of  honey 
to  the  branches  of  a  laurustine  ornamented  with  squares  of  white  and  blue 
paper  quickly  attracted  honey-bees,  which  went  first  to  the  colored  papers. 
Disconcerted,  they  began  an  agitated  search  for  the  honey  and  finally 
found  it. 

Perez's  critique  of  Plateau's  work. — Perez  pointed  out  that  the  use 
of  large  surfaces  of  colored  cloth  by  Plateau  to  demonstrate  the  indifference 
of  insects  to  color  was  incapable  of  furnishing  actual  evidence  on  this  point, 
since  insects  care  nothing  for  color  in  itself,  but  only  as  a  sign  of  the  food 
they  are  seeking.  The  same  failure  to  recognize  the  significance  of  the 
resemblance  of  small  bits  of  cloth  to  flowers  in  contrast  to  large  pieces  was 
regarded  as  vitiating  Plateau's  results  with  bright  standards  placed  near 
masked  composite  heads.  A  just  criticism  of  the  latter's  statement  that 
all  the  results  obtained  with  colors  were  illusory  because  of  Graber's  dis- 
covery, was  based  upon  the  fact  that  this  showed  insects,  like  man,  to 
receive  different  impressions  from  the  light  of  different  parts  of  the  spec- 
trum, and  that  it  is  immaterial  whether  their  perceptions  are  the  same  as 
ours,  since  they  possess  a  scale  of  luminous  sensations.  Experiment  based 
upon  the  use  of  colored  objects  is  legitimate  in  every  respect  and  to  proscribe 
it  would  be  only  to  carry  one's  scruples  to  excess.  Attention  was  also  called 
to  the  obvious  discrepancy  of  Plateau's  own  conclusions  as  to  the  importance 
of  color,  involved  in  the  two  statements,  "Neither  form  nor  color  seems 
to  have  any  attractive  role"  (1895),  and  "I  admit  that  this  vague  visual 
perception  can  guide  the  insect  toward  the  flower  mass,  concurrently  with 
smell  but  to  a  much  less  degree"  (1899). 

In  regard  to  the  errors  committed  by  pollinators,  P6rez  noted  that 
Plateau  invoked  smell  to  explain  the  attraction  of  flowers  containing  nectar, 


168  PRINCIPLES  AND  CONCLUSIONS. 

but  said  nothing  about  the  role  of  this  when  it  was  a  question  of  flowers 
already  visited,  or  of  faded  flowers,  buds,  or  fruits.  The  mistaken  visits 
to  these  were  said  to  be  directed  by  the  form,  poorly  seen,  the  attraction 
of  which  had  been  previously  denied.  In  the  case  of  withered  flowers  it 
was  thought  clear  that  these  were  really  visited  because  of  the  usual  similarity 
in  color  and  not  because  of  the  form,  as  was  likewise  true  in  the  case  of  many 
buds.  Imperfect  vision  of  form  can  not  serve  to  explain  the  majority  of  the 
errors  noted  by  Plateau,  and  form  is  to  be  regarded  as  the  least  important 
of  the  features  that  effect  attraction. 

Effect  of  colors  at  the  hive. — Theen  (1896:101)  summarized  the 
results  of  a  number  of  investigators  on  the  color  sense  of  bees,  including  the 
little  known  ones  of  Wiist  and  of  Donhoff.  In  Wust's  apiary  the  thresholds 
of  the  hives  were  painted  with  bright  colors,  which  stood  out  sharply  against 
the  deep-green  of  the  Ampelopsis  surrounding  them  on  three  sides.  On  one 
occasion  the  supply  of  bright  colors  was  inadequate  and  some  thresholds 
were  painted  black,  red,  or  blue.  The  consequence  was  that  the  bees 
required  a  longer  time  for  recognition  and  were  able  to  recognize  the  proper 
hive  at  once  only  after  the  second  day;  at  first  it  was  necessary  for  them 
to  orient  themselves  for  a  much  longer  time  in  order  to  determine  the  right 
hive.  He  also  found  that  queen-bees  were  best  equipped  with  the  sense 
of  location  and  color.  When  a  red  petal  of  a  poppy  was  placed  on  the  yellow 
threshold  of  a  hive,  a  returning  queen  approached  ten  times  as  though  to 
enter  and  even  alighted  twice;  it  then  quickly  flew  back,  showing  that  she 
recognized  the  place  accurately,  but  found  something  there  that  was  not 
present  when  she  flew  out.  Suddenly  she  flew  away  and  was  lost  to  view, 
and  the  red  petal  was  removed.  After  a  few  minutes  she  flew  directly  to 
the  threshold  without  hovering  about  and  immediately  disappeared.  Don- 
hoff pasted  blue  paper  before  a  hive  and  14  days  later  replaced  it  with  a 
yellow  one.  Bees  returning  from  the  field  hesitated  long  before  flying  to  the 
hive  and  finally  most  of  them  flew  to  another  part  of  the  hive  rather  than 
to  the  entrance.  Theen  also  cited  three  observations  of  Darwin,  in  which 
honey-bees  flew  directly  from  a  tall  larkspur  in  full  bloom  to  one  of  another 
species  at  a  distance  of  10  to  12  feet,  though  none  of  the  flowers  were  open 
and  the  buds  showed  but  a  tinge  of  blue. 

Critiques  of  Kienitz-Gerloff. — In  a  series  of  four  reviews,  Kienitz- 
Gerloff  considered  the  results  and  conclusions  adduced  in  the  five  papers 
of  Plateau's  first  series.  With  reference  to  the  response  to  masked  Dahlia 
heads  he  pointed  out  that  the  insects  were  readily  guided  by  the  sense  of 
smell,  and  that  this  did  not  warrant  the  assumption  that  the  color  of  the 
normal  heads  played  no  part  in  attraction,  especially  since  no  comparative 
number  of  visits  was  given  for  the  two  kinds  of  heads.  He  cited  the  many 
and  varied  experiments  of  Lubbock  and  of  Mueller,  and  in  particular  those 
of  Forel  with  insects  deprived  of  their  antennae  to  show  that  the  experiments 
with  Dahlia  were  not  to  be  regarded  as  adequate.  In  opposition  to  the 
conclusion  of  Graber  that  weakly  refrangible  light  gives  leucophobe  animals 
the  impression  of  darkness,  he  brought  forward  the  fact  that  all  nocturnal 
winged  animals  fly  to  lighted  windows,  indicating  that  they  are  drawn  by 
the  contrast  (1896: 123).    In  discussing  the  experiments  in  which  the  corolla 


RELATED  STUDIES  AND  CRITIQUES.  169 

was  removed,  he  emphasized  the  fact  that  the  mutilated  flowers  were  always 
near  normal  ones  and  the  insects  attracted  by  the  latter  were  guided  by 
odor  to  the  former.  Moreover,  control  numbers  were  lacking  in  most  cases 
and  in  that  of  Lobelia  were  mostly  against  the  assumption.  The  fact  that 
a  honey-bee  flew  to  faded  flowers  and  buds,  and  even  to  fallen  petals,  gave 
evidence  of  the  effect  of  color,  the  fact  that  it  took  nectar  only  from  the 
mutilated  flowers  being  explained  perhaps  by  the  greater  odor  and  accessi- 
bility. It  was  further  remarked  that  the  results  with  flowers  of  different 
colors  of  the  same  species  indicated  just  the  opposite  conclusion  to  that 
drawn,  as  shown  especially  in  the  case  of  Centaurea.  The  small  number  of 
experiments  were  regarded  as  having  little  weight  in  comparison  with  the 
observations  of  Mueller  on  5,674  visits  by  841  species  of  insects  to  422 
alpine  flowers.  Whether  insects  see  the  various  colors  as  we  do  or  not  is 
immaterial,  if  in  general  they  distinguish  them  (1897:84,  108). 

Plateau  was  further  criticized  for  not  being  familiar  with  Mueller's 
results  and  for  opposing  a  single  observation  on  Listera  to  the  many  made  by 
the  latter,  as  well  as  for  not  distinguishing  between  insects  of  different 
orders  and  diverse  intelligence,  although  Mueller  had  frequently  empha- 
sized the  importance  of  this.  Moreover,  he  should  have  repeated  the  experi- 
ments of  Lubbock  and  of  Mueller,  which  showed  that  insects  possessed  a 
clear  perception  of  color,  instead  of  trusting  too  much  to  the  evidence 
drawn  from  artificial  flowers.  Likewise,  he  contradicted  himself  when  he 
explained  the  visit  of  a  cabbage  butterfly  to  an  artificial  flower  on  a  lady's 
hat  by  saying  that  it  sought  the  flower  for  its  protective  white  color  and  not 
for  nectar.  The  critic  also  found  unconvincing  the  use  of  artificial  flowers 
made  from  leaves  and  provided  with  honey,  owing  to  the  superior  attraction 
of  honey,  irrespective  of  the  object  on  which  it  may  be  placed.  The  final 
conclusion  was  reached  that  Plateau  had  proved  nothing  against  the  color 
sense  of  insects,  although  it  was  admitted  that  odor  played  an  important 
r61e,  as  Mueller  had  long  before  insisted. 

Knuth's  critique. — The  results  of  Plateau's  first  series  were  reviewed 
by  Knuth  (1898,  1906:204),  who  pointed  out  that  they  permitted  another 
interpretation  than  that  given.  In  the  case  of  umbels  of  Heracleum  covered 
with  green  leaves,  the  visits  of  a  variety  of  insects  were  regarded  as  indi- 
cating that  insects  are  attracted  also  by  odor,  but  that  this  was  alone 
effective  was  not  proved,  since  there  was  no  comparison  with  the  visitors 
of  the  umbels  not  masked.  The  evidence  that  color  is  not  attractive, 
afforded  by  behavior  to  the  differently  colored  varieties  of  the  same  species, 
is  inconclusive  and  it  can  only  be  concluded  that  color  is  immaterial  in 
flowers  of  the  same  form.  The  experiments  in  which  honey  was  added  to 
bright  flowers  that  are  normally  little  visited  merely  prove  the  well-known 
fact  that  the  odor  of  honey  is  a  powerful  lure.  Since  both  honey-bees  and 
bumble-bees  distinguish  readily  in  many  cases  between  flowers  visited  and 
unvisited,  it  is  not  strange  that  they  distinguished  the  artificial  from  the 
natural  flowers  in  Plateau's  tests  and  left  them  alone,  even  when  supplied 
with  honey.  Neither  the  paper  flowers  nor  those  made  from  green  leaves 
and  provided  with  honey  prove  that  color  is  unattractive  to  insects,  but 
both  merely  emphasize  the  powerful  attraction  exerted  by  the  odor  of  honey. 


170  PRINCIPLES  AND  CONCLUSIONS. 

Since  other  odors  were  unattractive  or  actually  repellent,  with  the  exception 
of  thyme  and  sage,  which  were  weakly  attractive,  Plateau's  theory  is 
refuted  by  his  own  experiments. 

The  discovery  that  bees  still  visited  flowers  rendered  inconspicuous  by 
removing  the  petals  or  the  colored  part  of  the  corolla  seemed  at  first  to 
overthrow  the  accepted  principle  of  attraction  by  color.  However,  careful 
consideration  of  these  experiments  led  to  the  conclusion  that  Plateau's 
inferences  were  not  justified  and  that  another  explanation  was  permissible. 
The  mutilation  of  Digitalis  by  cutting  away  the  corolla,  together  with  the 
stamens  and  style,  to  leave  a  stump  only  1  cm.  long  seemed  to  warrant  the 
conclusion  that  neither  color,  size,  nor  form  was  essential  to  their  attraction. 
Knuth  argues,  however,  that  the  nectar  is  more  exposed  and  the  fragrance 
more  widely  diffused  and  that  this  compensates  for  the  loss  of  the  corolla; 
moreover,  the  visits  should  thus  have  been  more  numerous  than  to  the 
normal  flowers,  which  was  not  the  case.  With  other  species  the  mutilated 
flowers  were  visited  less  than  the  normal  ones,  a  fact  that  Knuth  regarded 
as  proving  that  the  corolla  also  plays  a  part  in  attraction.  In  the  case  of 
Antirrhinum  majus  the  lack  of  visitors  to  the  cut  flowers  seems  to  indicate 
that  the  odor  is  not  effective  and  that  the  form  and  color  of  the  corolla  play 
the  chief  part.  Moreover,  the  frequent  visits  of  Megachile  to  heads  of  Cen- 
taurea  cyanus  deprived  of  ray-flowers,  explained  by  Plateau  as  due  to  the 
odor,  may  be  equally  well  explained  by  the  memory  of  the  bee  as  applied  to 
the  honey-bearing  disk-flowers. 

Plateau  has  given  a  one-sided  meaning  to  his  experiments,  without  regard 
to  the  work  of  earlier  investigators.  Thus,  he  has  entirely  overlooked  the 
experiments  of  Forel,  who  showed  that  blinded  insects  are  unable  to  recog- 
nize the  landing-place  of  the  flower,  while  those  that  have  the  antennae 
cut  away  fly  confidently  from  flower  to  flower.  He  further  ignores  the 
results  of  Mueller,  Loew,  MacLeod,  and  Knuth  himself,  which  have  estab- 
lished the  following  principles: 

1.  Other  things  being  equal,  a  flower  is  visited  by  insects  in  proportion  to  its  conspic- 

uousness.  Among  related  species  that  agree  closely  in  form  and  color  as  well  as 
in  floral  mechanism,  the  most  conspicuous  receive  the  most  visits  and  the 
least  conspicuous  the  smallest  number. 

2.  In  a  number  of  cases  odor  has  more  to  do  with  the  attraction  of  insects  than  the 

color  and  size  of  the  corolla. 

3.  Dull  yellow  flowers  are  not  visited  as  a  rule  by  beetles,  while  nearly  related  flowers 

that  are  white  or  of  some  other  conspicuous  color  attract  these  insects  even 
when  nectarless.  Reddish-blue  or  violet  flowers  are  preferred  by  bees,  butter- 
flies, and  hoverflies,  which  are  highly  specialized,  while  the  most  frequent  visi- 
tors to  white  or  yellow  flowers  are  less  intelligent  insects  with  a  short  proboscis. 
Bumble-bees  appear  least  dependent  upon  the  color  of  flowers,  and  as  Mueller 
indicated,  are  influenced  more  by  food-value  than  by  the  external  appearance 
of  flowers. 

4.  Strong-smelling  flowers  attract  flies  more  particularly,   while  those    with   sweet 

aromatic  odors  attract  bees  strongly  without  excluding  other  insects.  The 
delicate  odor,  strongly  exhaled  toward  evening,  of  many  white  flowers  with 
long  corolla-tubes  attracts  hawk-moths  especially,  as  well  as  other  nocturnal 
Lepidoptera. 


RELATED  STUDIES  AND  CRITIQUES.  171 

"Plateau's  experiments  only  show  that  the  sense  of  smell  perhaps  guides  insects  to  a 
greater  extent  than  has  hitherto  been  supposed.  Apparently  there  is  need  of  further 
experiments  to  decide  questions  as  to  the  attraction  of  insects  to  flowers  by  means  of 
the  senses  of  smell  and  sight.  Meanwhile,  the  following  law  may  be  provisionally 
accepted:  Attraction  from  considerable  distances  is  certainly  effected  for  the  most 
part  by  the  odor  of  flowers,  which  fills  the  air  as  with  invisible  clouds  and  indicates 
the  direction  for  flight:  when  the  insects  approach  near  (1  to  2  meters),  the  colors  of 
flowers  undertake  the  task  of  attracting  them  further,  and  when  they  finally  settle,  the 
lines  and  points  long  since  described  by  Sprengel  under  the  name  of  'Saftmal'  (i.  e., 
sapmark)  serve  to  point  the  way  to  the  nectar." 

Reeker's  experiments  with  artificial  flowers. — Reeker  (1898:105) 
made  a  critical  review  of  Plateau's  first  series  of  investigations,  in  which  he 
brought  forward  essentially  the  objections  advanced  by  Kienitz-Gerloff  and 
by  Knuth.  Of  especial  interest  was  an  extract  from  Graber  which  showed 
that  Plateau  was  not  justified  in  citing  Graber 's  views  in  support  of  his 
conclusions,  since  the  latter  was  actually  an  exponent  of  the  color  sense  of 
insects  (p.  215).  In  the  first  experiment  Reeker  employed  artificial 
flowers  of  Centaurea  cyanus,  4  of  which  were  grouped  in  a  square  against 
a  green  background,  at  a  distance  of  6  to  8  meters  from  other  flowers.  Dur- 
ing an  hour  of  observation,  11  individuals  of  Pieris  inspected  the  imitations 
and  4  actually  alighted.  Honey-bees  were  very  scarce,  only  one  coming 
near  the  cornflowers,  and  this  landed  and  probed  for  nectar  for  2  seconds; 
3  syrphids  came  to  seek  pollen  and  6  to  8  small  flies  flitted  from  one  head 
to  another  in  an  assiduous  search  for  pollen  or  nectar.  For  the  second 
experiment  four  artificial  flowers  of  Ranunculus  acris  were  added  to  the 
cornflowers  in  a  fairly  compact  group,  placed  at  a  distance  of  12  meters  from 
natural  flowers.  Five  Pieris  made  inspections  and  3  others  alighted,  while 
one  bumble-bee  also  landed  on  a  cornflower  and  probed  for  nectar,  and  2 
honey-bees  visited  nearly  every  flower  in  the  group.  A  dozen  small  flies 
made  long  stays  at  several  flowers  and  flew  back  and  forth  from  the  blue 
to  the  yellow. 

Reeker  stated  that  these  experiments  gave  such  uniformly  positive  results 
that  further  investigation  seemed  unnecessary,  an  unfortunate  conclusion 
in  view  of  the  much  more  extensive  studies  of  Plateau.  He  regarded  them 
as  furnishing  incontrovertible  proof  that  the  color  and  form  of  flowers  serve 
to  attract  insects.  Granting  that  the  odor  of  flowers  constitutes  a  very 
powerful  means  of  attraction,  it  must  also  be  conceded  that  color  likewise 
has  a  share  in  the  attraction  of  pollinating  insects.  However,  Plateau 
(1906:87)  considered  it  very  probable  that  the  visits  noted  by  Reeker  were 
due  to  the  materials  entering  into  the  composition  of  the  artificial  flowers, 
such  as  starch,  etc. 

Decorollate  poppies. — In  order  to  demonstrate  the  importance  of  the 
corolla,  Giltay  (1900)  grew  Papaver  rhoeas  in  two  beds  of  about  equal  extent 
and  separated  50  meters  from  each  other,  and  in  a  third  bed  covered  by  a 
screen  impenetrable  to  pollinators.  In  the  first  two  the  number  of  flowers 
was  equalized,  and  in  one  the  flowers  were  left  to  develop  normally,  while 
in  the  other  the  corolla  was  removed  before  the  flowers  opened.  A  portion 
of  the  latter  were  later  fertilized  artificially  with  other  pollen  to  determine 
whether  the  mutilation  itself  could  influence  the  production  of  seed.     The 


172  PRINCIPLES  AND  CONCLUSIONS. 

plants  in  the  wire  cage  produced  only  a  very  small  amount  of  seed,  viz, 
0.004  mg.  per  flower,  although  they  had  been  artificially  pollinated.  The 
215  decorollate  flowers  yielded  10.77  gm.  of  seed  or  0.05  gm.  per  fruit,  while 
215  normal  ones  produced  25.23  gm.  or  0.117  per  fruit.  The  28  decorollate 
flowers  that  had  been  artificially  fertilized  gave  0.115  gm.  of  seed  per  fruit. 

The  criticisms  of  Plateau  as  to  the  methods  and  conclusions  of  Giltay 
have  already  been  given  (p.  159).  These  brought  in  return  a  critique  of 
Plateau's  studies,  in  addition  to  a  new  series  of  experiments  with  mutilated 
poppies,  in  which  especial  attention  was  devoted  to  the  insect  visitors 
(1904:368).  The  first  emphasized  the  discrepancy  between  Plateau's 
earlier  and  later  conclusions  as  to  the  importance  of  color,  as  Perez  had 
already  done,  and  summarized  the  experiments  of  Forel  with  masked  Dahlia 
heads,  which  gave  results  very  different  from  those  obtained  by  Plateau  (p. 
145).  Papaver  rhoeas  was  again  used  by  Giltay  for  his  studies,  owing  to  its 
many  advantages,  such  as  complete  sterility  to  its  own  pollen,  the  ease  of 
cultivation,  the  abundance  of  flowers  and  of  insect  visitors,  and  the  readiness 
with  which  the  corolla  may  be  removed.  To  insure  better  manipulation 
the  plants  to  be  used  were  transferred  to  pots  and  kept  in  a  screened  cage 
until  needed.  Checks  were  employed  in  connection  with  the  removal  of  the 
calyx  and  corolla  to  show  that  this  in  no  wise  affected  the  visits  of  insects 
and  that  Plateau's  fears  were  consequently  groundless.  In  the  first  series 
of  1902  two  potted  plants  were  placed  on  a  greensward  2  meters  apart, 
and  the  corollas  removed  from  the  flowers  of  one  of  them.  For  an  equal 
number  of  flowers  the  normal  ones  received  96  visits  and  the  mutilated  9 
visits,  while  the  second  series  with  the  plants  near  each  other  and  with  but 
one  or  two  flowers  each  gave  38  and  1  visits  respectively.  In  the  third 
series  the  intact  flowers  obtained  34  visits,  those  with  the  calyx  removed 
and  the  corolla  still  folded  14,  ordinary  buds  1,  and  young  fruits  2.  When 
flowers  were  so  masked  by  pots  that  they  could  not  be  seen  but  any  odor 
present  was  free  to  escape,  they  received  no  visits,  but  bees  came  readily  as 
soon  as  the  pot  was  removed.  When  the  pot  was  so  placed  that  the  flower 
was  visible,  it  received  frequent  visits,  thus  showing  that  the  odor  of  the 
pot  was  not  a  factor  in  the  preceding  case.  The  relative  importance  of 
color  and  odor  was  further  demonstrated  by  placing  petals  in  a  dish  and 
covering  them  with  a  pot  so  that  they  were  invisible  but  the  odor  could 
escape.  These  were  never  visited,  but  when  the  pot  was  removed,  bees 
alighted  on  them,  sometimes  immediately. 

Several  additional  series  of  experiments  were  carried  out  in  1903,  in  which 
the  response  to  the  two  kinds  of  flowers  was  shown  to  be  greatly  influenced 
by  habit.  At  first  when  one  or  more  pots  of  mutilated  flowers  were  placed 
among  normal  ones,  the  visitors  gave  the  former  practically  no  attention. 
In  the  case  of  two  flowers  of  each  sort  the  intact  received  15  visits,  the  muti- 
lated, none,  while  on  the  next  day  a  honey-bee  was  seen  that  went  to  muti- 
lated flowers  as  often  as  to  normal  ones.  Three  days  later  an  observation 
on  4  each  of  intact  and  decorollate  flowers  yielded  12  visitors  to  the  former 
and  none  to  the  latter,  and  1  flower  of  each  on  the  same  plant  gave  respec- 
tively 8  and  4.  However,  1  marked  honey-bee  went  to  18  intact  and  13 
mutilated  flowers.  When  all  the  flowers  in  the  experimental  plot  were  picked 
and  2  pots  with  equal  numbers  of  the  two  sorts  of  flowers  were  placed  at 


RELATED  STUDIES  AND  CRITIQUES.  173 

a  distance  of  several  meters,  the  bees  came  first  to  the  habitual  place  and 
flew  about  it  for  some  time  before  finding  the  potted  plants,  on  which  they 
went  only  to  the  normal  flowers.  When  the  latter  were  picked  and  placed 
in  water  or  wet  sand  near  the  plot,  there  were  several  times  as  many  visitors 
to  them  as  to  the  mutilated  flowers.  As  the  visitors  to  the  latter  increased, 
the  two  kinds  were  separated  about  2  meters,  with  the  result  that  24  honey- 
bees and  23  bumble-bees  went  to  intact  flowers  and  15  and  10  to  the  muti- 
lated ones.  When  the  flower  groups  were  again  brought  near  each  other, 
the  number  of  visitors  to  normal  flowers  alone  was  1  honey-bee  and  9 
bumble-bees,  to  mutilated  alone  16  honey-bees,  while  11  bees  and  1  Bombus 
went  first  to  a  normal  flower  and  2  of  the  latter  first  to  a  decorollate  one. 
The  12  mutilated  flowers  were  then  removed  to  a  distance  of  2  meters  and 
in  their  place  was  put  a  new  group  of  5  similar  ones;  the  latter  received  8 
visits,  while  a  single  bee  alone  found  the  flowers  in  the  new  position.  Fin- 
ally, the  position  of  a  single  flower  of  each  was  changed  each  time,  with 
the  results  that  14  visitors  came  to  the  intact  flower  to  3  for  the  decorollate 
one,  the  latter  being  visited  first  but  a  single  time.  When  the  intact 
flower  alone  was  shifted  it  still  received  all  the  visits,  but  when  the  two  were 
again  brought  together  the  sole  visiting  bee  went  10  times  to  the  intact 
flower  and  then  directly  to  the  mutilated  one.  The  normal  flower  was 
then  taken  away,  and  the  bee  now  visited  the  mutilated  one. 

In  the  second  series  of  experiments,  Giltay  (1906:468)  extended  the  work 
of  Perez  on  the  response  of  bees  to  red  flowers,  employing  geranium  and 
corn-poppy  for  this  purpose.  A  special  instrument  was  devised  for  catch- 
ing and  marking  bees,  and  practically  all  the  studies  were  made  with  bees 
so  treated.  The  results  of  the  experiments  are  expressed  in  a  number  of 
resume's,  as  well  as  in  the  final  summary.  Trained  bees  came  to  the  usual 
place  even  when  the  plant  used  was  not  provided  with  honey;  however, 
they  did  not  alight  or  for  but  a  moment,  though  they  landed  in  the  normal 
manner  as  soon  as  honey  was  placed  on  the  flowers.  When  a  plant  without 
honey  was  substituted  for  one  with  it,  and  the  latter  placed  at  a  distance 
of  1  to  2  meters,  most  of  the  first  visits  were  made  at  the  usual  place,  but 
the  honey  plant  was  quickly  found  again.  The  honey-free  plant  was  put 
2.5  meters  to  one  side  of  the  usual  place  and  the  honey-bearing  one  the 
same  distance  to  the  other  side;  several  bees  flew  about  the  experimental 
spot,  but  visited  neither  pot,  until  the  honey-bearing  plant  was  replaced, 
when  Nos.  5  and  4  visited  it  again.  Five  leaves  were  spread  with  honey  and 
placed  on  the  ground  below  the  honey-bearing  plant.  Within  a  few  min- 
utes, three  visits  were  made  to  the  latter  and  later  these  were  repeated, 
without  the  other  plant  or  the  honey-bearing  leaves  being  perceived.  This 
indicated  that  the  odor  of  the  honey  was  not  sufficiently  strong  to  be  attrac- 
tive at  the  short  distance  represented  by  the  height  of  the  geranium  plant. 
When  a  cork  with  honey  and  a  dish  of  the  same  were  placed  near  the  two 
plants,  both  the  latter  were  frequently  visited,  but  the  honey  alone  was  not 
noticed.  In  the  next  experiment,  a  blue  flower  of  iris  and  a  bud  of  poppy 
with  the  calyx  removed  were  put  a  meter  distant  on  opposite  sides  of  a 
honey-bearing  geranium,  but  neither  was  visited.  The  iris  was  then 
replaced  by  a  full-blown  poppy,  which  was  visited  by  both  bees.  When 
Brassica  was  employed,  it  was  also  visited,  though  to  a  less  degree  than 
the  geranium. 


174  PRINCIPLES  AND  CONCLUSIONS. 

In  the  studies  with  Pelargonium,  22  honey-bees  were  concerned,  20  of 
which  were  marked  and  brought  to  a  flower  provided  with  honey,  while  2 
made  independent  visits.  Of  the  22,  only  4  returned  to  the  place  of  experi- 
ment and  one  of  these,  No.  4,  more  often  than  all  the  others.  The  visitors 
to  the  honey-bearing  flowers  clearly  exhibited  place-memory,  as  well  as  a 
preference  for  these  over  those  without  honey,  and  the  ability  to  remember 
Pelargonium  after  they  had  once  learned  it.  During  14  days  of  experiment 
no  case  was  found  of  a  marked  bee  bringing  others,  the  only  doubtful  instance 
being  that  of  a  bee  that  seemed  to  come  by  mere  chance.  Perez  explained 
the  visits  ultimately  made  to  flowers  without  honey  as  due  to  the  memory- 
association  of  honey  and  color,  and  Giltay  also  found  such  visits  to  be 
numerous.  Moreover,  he  thought  that,  while  form  and  fragrance  might 
play  a  part  in  this,  it  was  improbable  that  these  could  be  perceived  as 
quickly  and  accurately  as  was  the  case.  His  conclusion  was  that  the 
bees  saw  the  flowers  of  Pelargonium  as  standing  out  against  the  back- 
ground of  different  color  and  consequently  could  easily  find  them  at  a  cer- 
tain distance. 

The  experiments  with  Papaver  were  designed  to  demonstrate  the  relative 
attraction  of  decorollate  flowers  or  of  paper  ones,  usually  with  a  natural 
center,  in  competition  with  normal  flowers.  These  were  organized  in  such 
a  manner  as  to  bring  out  clearly  the  effect  of  memory  of  place.  In  all 
cases  of  competition  between  decorollate  and  intact  flowers,  the  latter  were 
always  much  more  visited.  The  method  of  exposure  exerted  an  evident 
influence  upon  the  ratio,  since  the  decorollate  were  first  sought  after  the 
normal  flowers  had  been  brought  near  them.  As  in  the  experiments  of 
1903,  it  was  found  that  flowers  covered  with  a  pot  were  not  visited  when 
they  were  not  visible  from  the  outside.  In  the  case  of  paper  flowers  with 
natural  centers,  one  bee  visited  practically  all  of  these,  independently  of 
their  position,  while  another  was  much  more  timid,  flying  to  some  of  them, 
but  rarely  alighting.  However,  in  a  second  series,  the  first  bee  behaved 
in  a  wholly  inexplicable  manner,  going  to  both  the  normal  and  artificial 
flowers,  but  stopping  at  none,  until  it  finally  landed  on  a  yellow  composite 
one.  By  means  of  a  particular  grouping  it  was  possible  to  bring  the  bees 
to  visit  decorollate  flowers  readily,  though  to  see  the  latter  it  was 
almost  necessary  for  them  to  pass  very  close.  After  the  bees  had  been 
attracted  to  the  decorollate  flowers,  the  latter  were  exposed  with  an  intact 
one,  but  this  was  then  alone  visited. 

In  the  case  of  Papaver,  27  bees  were  marked,  of  which  13  returned  and  5 
served  for  experimental  purposes.  These  showed  place  memory  in  a  high 
degree.  Of  their  own  accord  they  found  the  decorollate  flowers  not  at  all 
or  only  by  chance,  when  these  were  not  exposed  in  a  most  conspicuous 
manner.  Once  attracted  to  them,  they  later  found  them  more  easily,  and 
often  returned  to  the  spot  where  the  flowers  had  stood  earlier.  Likewise, 
artificial  flowers  with  natural  centers  were  not  readily  visited,  but  they 
were  frequently  sought  after  the  bees  had  first  been  attracted  to  them. 
Marked  individual  differences  were  exhibited  by  the  bees  employed  in  the 
experiments,  and  the  same  bee  sometimes  behaved  in  two  opposite  ways. 

It  was  concluded  that  bees  are  certainly  attracted  by  the  corolla  in 
Pelargonium  and  Papaver,  and  that  it  is  very  improbable  that  a  special  odor 


RELATED  STUDIES  AND  CRITIQUES.  175 

constitutes  the  attraction  of  this  organ.  Since  a  single  petal  or  a  bud 
deprived  of  its  calyx  exerts  this  attraction,  it  can  not  depend  upon  the  form 
of  the  flower.  Hence,  it  must  be  due  to  the  color,  which  must  also  stand 
out  sharply  from  the  background  to  the  bee's  eye,  although  it  can  not 
be  said  that  they  see  the  color  red  as  we  do.  Small  amounts  of  honey  had 
relatively  little  effect,  at  equal  distances  a  single  corolla  exercising  a  much 
stronger  power  of  attraction  than  a  quantity  of  honey  much  greater  than 
that  ever  found  in  a  single  flower. 

Response  to  color  and  odor  by  a  hawk-moth. — The  experiments 
performed  by  Gorka  (1900:57),  though  few  in  number,  are  among  the  most 
important  of  all,  as  they  were  carried  out  with  newly  hatched  moths  in 
which  either  the  antennse  or  the  eyes  were  rendered  useless.  He  noted  that 
Deiliphila  elpenor,  which  was  frequent  in  a  garden  in  upper  Hungary, 
sought  the  flowers  of  Phlox  paniculata  and  drummondi  with  especial  fond- 
ness, but  ignored  the  other  flowers,  such  as  Dianthus,  Malva,  Borrago, 
etc.  As  a  preliminary  test,  a  butterfly  was  released  from  its  pupal  case, 
when  it  flew  straightway  to  Phlox.  On  this  he  based  his  experiments  to 
determine  whether  this  flower  attracted  hawk- moths  by  means  of  its  color 
or  its  fragrance.  For  this  purpose  he  had  at  his  disposal  about  40  pupae. 
The  antennae  of  three  hawk-moths  that  had  just  emerged  were  covered  with 
collodion  and  thus  deprived  of  the  sense  of  smell.  These  were  freed  in  the 
evening,  when  they  flew  directly  to  the  Phlox  at  a  distance  of  about  2  meters 
and  at  once  began  to  suck  the  nectar.  Four  days  later  the  eyes  of  4  hawk- 
moths  just  hatched  were  covered  with  shellac,  but  the  antennae  were  not 
disturbed.  In  the  evening  when  released,  these  flew  to  the  flowers  of 
Borrago  and  Malva,  which  they  immediately  left;  they  finally  landed  on 
those  of  Phlox,  where  they  remained  for  some  time.  They  then  flew  away,  but 
only  to  return  for  six  different  visits.  These  two  experiments  were  repeated 
12  times,  and  always  with  the  same  results.  In  three  cases  the  blue  flowers 
of  Borrago  were  sprinkled  with  essence  of  jasmine,  when  it  was  found  they 
were  no  longer  disdained,  but  were  visited  by  several  of  the  moths. 

Gorka's  results  prove  conclusively  that  the  hawk-moth  is  guided  by  both 
sight  and  smell,  and  indicate  that  the  former  is  more  directive  at  a  distance. 
Taken  in  conjunction  with  the  similar  experiments  of  Forel  (p.  140),  and 
Mayor  (p.  159),  they  afford  convincing  evidence  of  the  importance  of  both 
senses  in  regard  to  attraction. 

Vexillary  nature  of  the  plume  in  Muscari. — In  order  to  test  the 
value  of  Plateau's  conclusion  as  to  the  role  of  vexillary  organs,  Ferton 
(1901:96)  mutilated  racemes  of  Muscari  comosum  by  removing  the  sterile 
flowers,  which  form  a  vivid  violet-blue  plume  at  the  top  of  the  inflorescence. 
The  fertile  flowers  are  brownish  and  rather  inconspicuous,  but  they  emit  a 
pleasant  fragrance.  Andrena  vetula  flew  indifferently  to  the  fertile  or  sterile 
portion  of  normal  clusters,  but  when  the  fertile  flowers  were  cut  off,  it  went 
to  the  sterile  plume  direct,  then  dropped  to  the  level  of  the  fertile  ones, 
only  to  find  them  gone.  It  twice  hovered  for  some  time  before  the  muti- 
lated stem,  and  also  visited  two  or  three  such  clusters  in  succession.  Bom- 
bylius  fimbriatus  likewise  went  to  the  vivid  sterile  group  first  and  then 
descended  slowly  along  the  stem,  with  the  ligule  extended,  but  finally  dis- 


176  PRINCIPLES  AND  CONCLUSIONS. 

appeared  as  though  disconcerted.  Osmia  tricornis  and  some  males  of 
Anthophora  acervorum  were  not  deceived  by  the  change,  but  one  male 
visited  in  succession  four  mutilated  clusters  before  flying  away.  In  the 
following  experiment  the  colored  plume  was  removed  from  most  of  the 
plants  and  placed  on  the  ground  near  normal  ones.  A  female  of  this  species 
passed  by  the  latter  in  spite  of  their  fragrance  and  went  directly  to  one  of 
the  detached  clusters.  However,  it  quickly  recognized  its  error  and  de- 
parted after  visiting  one  of  the  fertile  flowers.  These  results  were  thought 
to  confirm  the  vexillary  role  of  the  plume,  which  was  regarded  as  a  better 
guide  than  the  perfume  which  diffused  in  all  directions.  When  the  essential 
organs  were  excised  from  flowers  of  Cistus,  such  blossoms  were  visited  by 
Anthophora,  in  spite  of  the  fact  that  the  fragrance  had  disappeared,  one 
individual  going  to  three  or  four  after  failing  to  find  pollen  in  the  first 
(cf.  Knoll,  1921). 

ForePs  experiments  with  covered  dahlias  and  with  artefacts. — 

Forel  (1901:26,  1904:22)  repeated  Plateau's  experiments  with  concealed 
dahlia  heads  in  order  to  check  his  conclusions.  A  bed  of  variously  colored 
dahlias,  much  visited  by  honey-bees,  contained  about  43  heads,  of  which  28 
were  covered  with  grape  leaves  fastened  below  by  pins;  in  4  heads  the 
yellow  center  alone  was  covered,  while  in  a  single  one  the  center  was  free 
and  the  rays  masked.  Forthwith  the  bees  ceased  to  visit  the  completely 
concealed  heads,  but  went  to  the  one  with  the  rays  covered  just  as  to  the 
normal.  They  also  flew  frequently  to  the  heads  with  masked  disk,  but 
soon  forsook  them,  though  a  few  succeeded  in  crawling  beneath  the  leaf. 
Just  as  soon  as  the  leaf  was  removed  from  a  red  dahlia  the  bees  returned 
to  it,  and  a  poorly  covered  head  was  also  discovered  and  visited.  Later  one 
bee  found  an  entrance  to  a  concealed  head,  to  which  it  repeatedly  returned. 
Various  individuals  continued  to  seek  the  dahlias  that  had  so  suddenly 
disappeared  and  late  in  the  afternoon  some  of  them  had  discovered  the 
hidden  flowers.  They  were  soon  imitated  by  the  others  and  in  a  short  time 
the  concealed  heads  were  again  regularly  visited.  As  soon  as  a  bee  had 
discovered  the  entrance  to  a  masked  head,  it  flew  without  hesitation  to  it 
on  subsequent  journeys.  Single  bees  were  not  noticed  by  the  others,  but 
a  successful  visit  by  several  brought  the  others  after  them.  It  was  con- 
cluded that  Plateau's  methods  were  faulty  and  his  results  erroneous,  due 
to  the  fact  that  he  had  failed  to  reckon  with  the  bee's  memory  and  attention. 

Three  days  later  crude  imitations  of  dahlia  heads  were  made  by  putting 
yellow  Hieracium  heads  in  Petunia  flowers  and  these  were  placed  among  the 
dahlias.  Neither  Petunia  nor  Hieracium  was  visited  by  the  bees,  though 
at  first  nearly  as  many  flew  to  the  artefacts  as  to  the  normal  heads.  They 
left  them  immediately,  however,  upon  finding  their  error,  obviously  through 
the  sense  of  smell.  They  behaved  in  the  same  manner  at  dahlias  with  the 
center  replaced  by  a  Hieracium  head.  As  a  check  a  beautiful  fragrant 
dahlia  disk  was  placed  among  some  white  and  yellow  Chrysanthemums 
neglected  by  the  bees.  For  a  half-hour  this  remained  unnoticed  by  the 
many  bees,  but  came  to  be  visited  like  the  normal  ones  as  soon  as  one 
or  two  had  discovered  it. 

In  confirmation  of  Plateau's  results,  Forel  found  that  the  most  carefully 
made  artificial  flowers  were  entirely  neglected  when   placed  among  the 


RELATED  STUDIES  AND  CRITIQUES.  177 

dahlias.  He  then  made  a  series  of  crude  paper  flowers  as  follows,  placing 
a  drop  of  honey  on  each;  (a)  red,  (6)  white,  (c)  blue,  (d)  blue  with  yellow 
center  made  from  a  dead  leaf,  (e)  rose-colored  with  a  dry  dahlia  disk, 
together  with  an  (/)  unchanged  green  dahlia  leaf.  During  the  first  hour 
the  honey  was  removed  from  the  blue  flower  alone.  The  red  flower  was 
then  brought  repeatedly  to  the  attention  of  a  bee  resting  on  a  dahlia, 
when  it  began  to  sip  the  honey.  This  bee  was  marked  with  blue,  and  those 
led  to  sip  from  the  white  and  the  rose  flower  were  painted  yellow  and  white 
respectively.  Upon  returning  from  the  hive,  the  blue  bee  flew  at  once  to 
the  red  flower  and  hovered  over  it  doubtfully,  then  visited  the  blue,  and 
went  again  to  the  red  but  not  to  the  dahlias.  The  yellow  bee  next  revisited 
the  white  flower,  then  visited  the  red  and  the  blue,  but  gave  no  heed  to  the 
normal  ones.  It  was  followed  by  the  white  bee,  which,  failing  to  find  the  rose 
flower  at  once,  began  to  work  on  the  dahlias,  but  remained  only  a  moment 
on  each.  It  returned  to  the  artefacts  without  finding  the  honey,  until 
it  encountered  a  corner  of  the  rose-colored  flower  and  began  to  sip.  After 
this  the  three  painted  bees,  and  no  others,  returned  regularly  to  the 
artefacts  and  ceased  to  visit  the  dahlias.  It  is  significant  that  they  dis- 
covered the  other  artificial  flowers  by  themselves,  doubtless  through  an 
instinctive  inference  from  analogy,  in  spite  of  the  fact  that  these  were 
somewhat  distant  from  each  other  and  differently  colored.  The  blue  bee 
went  to  red,  white,  and  both  blue  flowers,  the  yellow  to  white,  red,  blue, 
and  blue  composite,  and  the  white  to  rose,  red,  white,  and  blue  com- 
posite, the  green  not  being  found,  evidently  because  of  its  color. 

Finally,  a  new  bee  came  to  the  blue  composite  and  was  marked  with 
carmine,  after  which  she  drove  the  blue  bee  from  the  red  flower.  Another 
bee  came  to  the  rose  flower  and  was  painted  with  orange,  and  still 
another  to  the  white  flower  and  was  painted  green.  The  experiment  had 
now  lasted  more  than  three  hours  and  but  six  bees  had  come  to  know  the 
artefacts,  the  great  number  continuing  to  visit  the  dahlias.  Soon,  however, 
the  others  began  to  come  and  it  was  necessary  to  replenish  the  honey 
constantly,  a  swarm  finally  removing  the  last  traces  and  one  bee  discovering 
it  on  the  green  leaf.  After  vainly  searching  the  empty  artefacts,  the  bees 
began  to  return  to  the  dahlias;  at  this  moment  the  red  and  white  flowers 
were  replaced  by  red  and  white  paper  entirely  free  from  any  odor  of  honey. 
These  pieces  of  paper  were  visited  and  examined  by  various  bees,  still 
possessed  with  the  idea  of  honey,  the  white  bee  carefully  searching  the 
white  paper  for  three  or  four  minutes.  This  could  only  be  explained  by 
an  association  of  space,  form,  and  color  memories  with  memories  of  taste. 
When  the  artefacts  were  carried  away,  several  bees  followed  and  tried  to 
alight  on  them,  in  response  to  color  and  form  alone,  the  space-image  having 
changed. 

This  and  other  experiments  were  considered  to  demonstrate  the  space, 
form,  and  color  perceptions  of  the  honey-bee,  its  memory  particularly  with 
respect  to  vision  and  taste,  the  power  of  associating  gustatory  and  visual 
memories,  the  instinctive  ability  to  draw  inferences  from  analogy,  a  poor 
olfactory  sense,  a  one-sided  and  narrow  range  of  attention,  the  rapid  for- 
mation of  habits,  and  the  limited  imitation  of  bees  by  each  other.  Further 
experiments  designed  to  lead  the  bees  to  distinguish  between  disks  of  dif- 


178  PRINCIPLES  AND  CONCLUSIONS. 

ferent  color  were  vitiated  by  the  bees'  power  of  memory,  the  marked  bees 
placed  on  the  blue  disks  beginning  at  once  to  investigate  all  the  other  colors 
with  and  without  honey,  and  being  followed  by  a  swarm  that  even  besieged 
the  paint-box. 

Response  of  Syritta. — Schroder  (1901: 181)  recorded  12  cases  in  which 
a  honey-bee  approached  to  within  2  dm.  of  heads  of  Chrysanthemum  leu- 
canthemum  and  then  flew  to  a  bush  of  jasmine  at  a  distance  of  4  meters, 
the  strong  fragrance  of  which  was  carried  across  the  former.  He  clipped  the 
rays  from  half  a  group  of  12  heads  and  found  that  Syritta  pipiens  in  the 
course  of  a  half-hour  visited  37  normal  heads,  while  it  completely  ignored 
the  mutilated  ones.  Syritta  hovered  over  the  latter  a  longer  time  than  usual, 
but  without  alighting.  During  the  afternoon,  4  visits  were  made  to  the 
clipped  heads  and  21  to  the  normal,  and  on  the  next  day  19  to  46,  the  fly 
no  longer  showing  the  hesitation  before  the  former.  This  indicated  that  the 
insect  recognized  the  difference  in  the  heads  in  spite  of  the  similar  odor,  and 
that  it  learned  rather  rapidly  to  accustom  itself  to  the  mutilated  ones.  Two 
days  later  the  latter  were  cut  off  and  a  flat  piece  of  white  paper  the  size  of 
the  head,  provided  in  the  middle  with  another  piece  the  size  and  color  of  the 
disk,  was  fastened  on  the  end  of  the  stem.  In  spite  of  visits  to  the  normal 
flowers,  no  Syritta  paid  the  slightest  attention  to  these  crude  imitations, 
which  lacked  the  form  and  fragrance  of  real  flowers.  They  were  then 
furnished  with  a  few  drops  of  an  infusion  of  Chrysanthemum  heads,  but, 
while  they  were  inspected  during  the  next  half-hour,  no  Syritta  visited  them. 
However,  when  three  of  them  were  provided  with  honey,  they  received  10 
visits  during  the  half -hour  to  12  for  the  normal  ones.  The  other  three  were 
also  visited  four  times,  indicating  that  Syritta  had  again  profited  by  experi- 
ence. Three  artificial  flowers  made  of  cloth  were  fastened  on  the  stem  ends, 
and  one  received  a  visit,  but  it  was  thought  this  might  be  due  to  the  odor 
of  the  adjacent  normal  heads.  To  give  them  a  distinctive  odor  they  were 
soaked  in  the  infusion  of  normal  heads,  dried,  and  again  attached,  when 
they  received  7  visits  in  comparison  to  24  for  the  normal.  Thus,  the  question 
of  the  means  by  which  flowers  attract  insects  seemed  not  solved  in  the  direc- 
tion of  Plateau's  views. 

Andreae's  experiments  with  artificial  flowers.— In  a  comprehensive 
examination  of  Plateau's  results,  Andreae  carried  out  many  experiments 
with  artificial  flowers,  some  of  these  being  made  at  Jena  and  some  at  Lake 
Como  (1903:427).  In  the  first  series  yellow  artificial  flowers  were  placed 
2  meters  from  a  bed  of  Eranthis  nivalis  and  these  were  visited  during  an 
hour  by  10  honey-bees.  As  a  check  a  bell-glass  was  put  over  one  plant  to 
eliminate  the  influence  of  odor,  but  in  spite  of  this  4  honey-bees  came  to  the 
glass.  When  the  imitations  were  replaced  they  were  visited  8  times  within 
the  hour.  A  further  check  was  obtained  by  putting  10  decorollate  flowers 
in  one  beaker,  10  normal  ones  in  a  second,  and  the  detached  perianths  in 
a  third.  One  honey-bee  flew  into  the  first  glass  and  2  hovered  about  it, 
14  into  the  second  and  10  about  it,  and  9  into  the  beaker  with  perianths 
alone  and  4  about  it.  When  a  dark  paper  was  placed  upon  a  small  group 
of  Crocus  and  an  artificial  flower  placed  2  meters  away,  bees  went  to  the 
latter,  to  Crocus,  and  again  to  the  imitation  before  flying  away  to  the  snow- 


RELATED  STUDIES  AND  CRITIQUES.  179 

drop.  A  bell-glass  was  next  put  over  the  Crocus  flowers  and  5  honey-bees 
came  to  it  within  an  hour.  At  a  distance  of  a  meter  from  a  bed  of  yellow 
Crocus  was  placed  a  striking  artificial  flower  of  the  same  color  and  at  the 
same  distance  a  beaker  with  5  normal  flowers,  while  a  meter  further  away 
stood  one  with  10  similiar  flowers.  The  latter  was  surrounded  by  dark 
paper  with  a  fairly  large  opening  above,  so  that  the  odor  might  easily 
escape.  However,  not  a  single  bee  came  to  this  during  two  and  a  half 
hours,  though  10  visited  the  imitation  during  the  first  hour.  The  open  glass 
with  normal  flowers  was  constantly  visible,  but  only  one  bee  entered  it. 
The  next  installation  consisted  of  a  beaker  filled  with  blue  Crocus  2  meters 
from  the  bed,  another  with  white  Crocus  at  4  meters,  and  an  artificial  flower 
at  7  meters.  During  a  quarter  of  an  hour  these  received  respectively  11,  9, 
and  2  visits  by  honey-bees;  when  the  beakers  were  turned  down  they  still 
received  9  and  7  visits  respectively. 

In  the  first  experiment  with  Rhododendron  ciliatum  a  large  empty  beaker 
was  placed  2  meters  from  the  bush  and  a  smaller  one  filled  with  normal 
flowers  of  this  species  at  a  distance  of  3  meters,  the  first  designed  to  show 
the  effect  of  the  brightness  of  the  glass,  the  second  that  of  color.  During 
a  half-hour  but  2  bees  went  to  the  empty  beaker,  while  12  flew  to  the  red 
flowers  in  the  other,  and  10  flew  directly  against  the  glass  itself.  When 
this  beaker  was  inverted,  7  bees  went  to  it  in  5  minutes.  The  second  instal- 
lation consisted  of  three  beakers  placed  8  meters  from  the  bush  and  likewise 
distant  from  each  other,  one  containing  honey,  another  slightly  perfumed 
water,  and  the  third  was  the  inverted  one  with  normal  flowers,  designed 
to  show  the  relative  attraction  of  honey,  perfume,  and  color.  The  visits 
made  by  Musca  and  Apis  were  respectively  15  and  4,  12  and  3,  and  16  and 
10,  during  an  hour.  An  inverted  beaker  with  normal  flowers  gave  60  visits 
to  a  single  one  for  an  empty  beaker.  The  bush  was  then  shaken  and  20 
bees  flew  directly  to  the  normal-flower  beaker,  and  during  three  repetitions 
not  a  single  bee  went  to  the  empty  glass.  This  showed  conclusively  that 
the  bees  were  not  attracted  by  the  brightness  of  light  but  only  by  the  color 
itself.  Moreover,  the  honey-bee  must  be  able  to  see  color  for  a  distance 
of  8  to  10  meters  at  least.  When  the  attraction  of  honey  alone  was  tested, 
a  single  bee  came  to  the  beaker  as  though  by  accident. 

Parallel  to  a  bed  of  primroses  were  installed  a  yellow  primrose  made 
of  cloth,  an  inverted  beaker  containing  blue  primroses,  a  glass  of  honey,  and 
an  upiight  beaker  filled  with  the  same  flowers  freshly  picked.  The  last  two 
were  surrounded  with  dark-gray  paper  to  conceal  their  contents,  and  all 
were  placed  a  meter  from  the  bed.  The  artificial  flower  received  a  total 
of  18  visits,  of  which  10  were  made  by  the  honey-bee,  the  inverted  beaker  13, 
the  glass  of  honey  none,  and  the  open  beaker  1,  giving  a  ratio  of  31:1  in 
favor  of  color.  In  the  check  a  glass  with  diluted  honey  was  surrounded  with 
paper  and  placed  at  a  meter  from  the  bed,  while  at  2  meters  were  located 
an  imitation  flower  and  an  inverted  beaker.  This  yielded  26  visits,  14  by 
Apis,  to  the  artificial  flower,  2  to  the  beaker,  and  3  to  the  honey  glasses, 
or  28  to  3  in  favor  of  color.  The  second  check  consisted  of  four  glasses, 
one  filled  with  honey  and  the  other  three  with  primroses  and  all  wrapped 
with  dark  paper,  placed  at  a  meter  from  the  bed.  At  3  meters  were  located 
a  false  flower  and  an  inverted  beaker  of  red  primroses.     The  imitation 


180  PRINCIPLES  AND  CONCLUSIONS. 

received  38  visits,  25  by  bees,  the  inverted  beaker  17,  and  the  four  "odor" 
glasses  but  one,  giving  a  ratio  of  55 : 1  in  favor  of  color.  Even  when  the 
artificial  primrose  was  placed  5  meters  from  the  flower-bed,  it  received  13 
visits  from  bees  to  none  for  the  more  accessible  "odor"  glasses.  To  deter- 
mine the  effect  of  a  difference  in  form  the  artificial  primrose  was  re- 
placed by  a  peony  of  the  same  material  and  color,  which  was  placed  7 
meters  from  the  bed  of  primroses.  One  meter  from  the  latter  stood  four 
glasses,  one  filled  with  honey,  the  other  three  faintly  perfumed  with  jas- 
mine, mignonette,  and  violet  respectively.  However,  the  latter  obtained 
no  visits  in  contrast  to  41  for  the  imitation  flower. 

Twelve  meters  from  a  bush  of  Doronicum  caucasicum,  a  yellow  composite 
actively  sought  by  various  insects,  was  located  an  artificial  flower-bed 
composed  of  the  primrose  and  peony  already  used  and  an  orange-red  and  a 
dark-red  poppy,  all  of  which  were  a  meter  apart.  As  an  additional  attrac- 
tion, artificial  cornflowers  and  snowballs  were  placed  in  the  center  of  the 
square.  The  yellow  peony  received  31  visits,  the  orange-red  poppy  9, 
the  dark-red  one  3,  the  central  group  7,  and  the  primrose  but  1,  showing 
a  clear  relation  between  conspicuousness  and  attractiveness.  A  further 
test  of  the  effect  of  odor  was  made  by  filling  an  inverted  beaker  with  fresh 
primroses,  so  that  they  were  plainly  visible,  while  a  bell-glass  was  likewise 
filled  with  several  hundred  fragrant  flowers  of  the  same  species,  but  these 
rendered  invisible  by  means  of  dark  paper.  In  spite  of  the  advantages 
given  the  latter,  it  received  but  3  visits  to  35  for  the  former. 

When  5  funnels  were  filled  with  fragrant  flowers  of  the  peony  and  sur- 
rounded with  paper,  and  placed  above  the  bush,  now  past  blooming,  they 
received  but  3  visits  in  competition  with  a  bell-glass  in  which  several 
flowers  were  visible,  this  yielding  40  visits.  To  test  the  effect  of  the  glass 
itself,  the  same  bell-glass  full  of  peonies  was  placed  15  meters  away,  while 
a  small  empty  one  was  put  but  a  meter  distant.  The  latter  received  no 
visits  to  5  for  the  former.  In  the  next  trial  two  artificial  flowers  were  made 
of  bright-yellow  and  rose-red  tissue  paper,  provided  with  dark-green  below 
to  furnish  a  contrast,  and  attached  to  stakes  2  meters  high.  Within  a 
period  of  2  hours  17  visitors  went  to  one  and  16  to  the  other,  the  total  of  33 
including  12  bees.  When  a  yellow,  a  dark-yellow,  and  a  purple-red  cloth 
flower  were  employed,  the  yellow  obtained  21  visits  and  the  red  9,  during 
3  hours.  In  the  next  case,  3  flowers  of  Papaver  orientalis  were  placed  in  a 
funnel  so  that  the  odor  could  escape  without  their  being  seen,  while  to  the 
single  normal  flower  left  on  the  plant  was  added  a  larger  artificial  one  of 
cloth,  in  order  to  determine  whether  conspicuous  color,  color  and  odor, 
or  the  latter  alone  would  be  most  effective.  The  results  showed  81  visits 
to  the  imitation,  chiefly  by  Osmia  and  Apis,  56  to  the  normal  flower,  and 
none  to  the  funnels.  In  the  control  the  last  normal  flower  was  added  to 
those  in  the  funnel  and  this  placed  5  meters  distant  against  the  wind.  In 
spite  of  this  it  received  no  notice  from  the  bees,  which  meanwhile  made 
43  visits  to  the  imitation. 

Experiments  with  flowers  of  dull  color  but  nectar-bearing  showed  that 
the  color  was  often  attractive,  sometimes  more  attractive  than  the  odor 
of  nectar  or  honey.  Studies  were  also  made  of  flowers  with  dull  color  and 
marked  perfume,  such  as  Reseda,  Dahlia,  etc.    When  stems  of  the  former 


RELATED  STUDIES  AND  CRITIQUES.  181 

were  put  in  a  dark-brown  bag  of  gauze  and  hung  above  the  bed,  they  were 
visited  by  Prosopis  and  Andrena,  but  Apis  continued  to  work  only  on  the 
plants  in  the  bed.  In  the  case  of  bell-glasses  filled  with  mignonette  and  one 
of  them  inverted,  Prosopis  and  Andrena  went  only  to  the  one  with  the  open- 
ing, thus  exhibiting  the  reverse  response  to  odor  and  color  from  that  of  the 
higher  apids.  When  artificial  flowers  of  Paeonia  and  Primula  were  placed 
in  a  meadow,  8  Apis  went  directly  to  the  more  conspicuous  peony  and  one 
each  of  Apis  and  Bombus  to  the  primrose.  A  box  was  covered  on  the  four 
sides  with  differently  colored  cloths,  through  which  a  large  opening  per- 
mitted the  air  to  move.  When  linden  flowers  were  placed  on  the  inside, 
about  20  individuals  of  Prosopis  went  directly  in,  while  3  Eristalis  went  first 
to  the  color  before  entering,  and  10  to  20  A  pis  flew  against  the  color  alone, 
especially  on  the  lighted  side.  With  buckwheat  substituted  for  linden,  the 
results  were  the  same,  Apis  flying  to  the  color  and  Prosopis  entering  the 
box,  but  when  the  latter  was  empty,  Prosopis  failed  to  appear,  Apis,  how- 
ever, behaving  as  before.  In  the  case  of  a  choice  between  the  colored  bracts 
of  Salvia  horminum  and  artificial  cornflowers  attached  to  the  plant,  the 
former  received  20  visits  to  9  for  the  latter. 

A  few  weeks  later  experiments  with  Dahlia  variabilis  were  made  in  a 
garden  at  Cadenabbia  on  Lake  Como.  Four  heads  were  cut  off  and  laid 
in  a  pot  wrapped  with  green  paper,  which  was  kept  covered  until  the  odor 
had  time  to  collect,  and  at  the  same  time  a  large  bright-yellow  paper  flower 
was  fastened  to  the  stem.  The  pot  received  no  visits,  while  19  were  made 
to  the  imitation,  and  the  results  were  similar  when  other  paper  flowers 
were  employed.  When  red-brown  plums  were  placed  in  a  pot  and  also  on 
the  ground,  the  latter  alone  were  visited  by  honey-bees;  with  those  on  the 
ground  removed  and  the  pot  in  full  sunshine  the  odor  of  the  plums  attracted 
but  one  bee  in  the  course  of  an  hour.  Near  a  plum  tree  sought  by  hundreds 
of  bees  was  placed  a  pot  wrapped  with  bright  paper  and  filled  with  crushed 
ripe  plums,  and  a  paper  flower  with  contrast  colors.  The  latter  received  16 
direct  flights,  while  the  former  was  visited  only  by  young  bees  that  grazed  it  in 
flight.  In  the  last  experiment  with  diurnal  insects,  50  paper  flowers  of 
various  colors  were  fastened  to  stems  of  Zinnia  elegans,  and  the  normal  ones 
inclosed  in  wire-gauze  to  permit  the  attraction  of  fragrance  alone.  However, 
the  latter  received  no  visits,  while  the  former  had  49,  of  which  Apis  made 
30,  Argynnis  14,  Pieris  3,  and  Vanessa  2,  showing  that  the  butterflies  be- 
haved essentially  like  the  higher  bees. 

Andreae's  conclusions. — It  is  evident  that  running  insects  will  have 
the  sense  of  smell  better  developed,  while  flying  ones  that  possess  an  ex- 
tended life-period  have  sight  developed  in  proportion  to  their  rapidity 
of  flight.  Thus,  it  is  necessary  to  distinguish  between  high  and  low  types, 
the  one  characterized  by  long  direct  flight,  a  relatively  long  life-period, 
and  a  keen  sense  of  sight,  the  other  by  short  flight,  short  rife-period,  marked 
sense  of  smell  and  a  poorer  vision.  Consequently,  the  various  inflores- 
cences and  corollas  with  bright  colors  are  chiefly  adapted  to  the  biologically 
highly  differentiated  insects,  and  the  fragrant  flowers  without  bright  colors 
are  designed  to  attract  the  lower  ones.  Thus,  Prosopis  and  Andrena  react 
to  odors  very  differently  from  the  higher  apids,  for,  while  colors  attract 
Apis,  Osmia,  Anthophora,  and  Anthidium  from  considerable  distances,  as 


182  PRINCIPLES  AND  CONCLUSIONS. 

can  be  determined  by  their  direct  and  rapid  flight  to  them,  the  flight  by  the 
lower  types  is  quite  different.  The  latter  change  in  direction  and  each 
time  toward  the  side  from  which  the  fragrance  comes.  Such  insects  also 
perceive  colors,  but  only  when  they  are  near  at  hand.  Similar  differences 
also  occur  among  Diptera;  Eristalis  responds  differently  to  a  color  than  a 
gnat  does,  and  Bombylius  and  Volucella,  two  highly  developed  flies,  show 
but  very  slight  response  to  odor,  as  Forel  has  already  shown. 

The  conclusion  that  color  attracts  the  biologically  higher  insects  from  a 
distance  and  odor  when  near  at  hand  is  supported  not  only  by  the  experi- 
ments recorded,  but  also  by  the  following  facts.  A  brightly  colored  object 
does  not  change  its  position,  and,  if  forced  out  of  it,  becomes  more  or 
less  conspicuous  only  as  a  result  of  changes  in  lighting,  while  odor  behaves 
very  differently.  In  the  first  place,  its  intensity  varies  from  time  to  time, 
in  the  second  its  conveyance  depends  upon  a  variable  wind  direction,  and  in 
the  third  its  perception  is  determined  by  the  amount  of  humidity  in  the 
air,  since  the  antennae  are  much  more  sensitive  in  moist  than  in  dry  air. 
There  are  constantly  many  odors  in  the  atmosphere  which  pervade  and 
replace  each  other,  and  are  constantly  changing  their  position  in  response 
to  the  slightest  breeze.  Thus,  the  view  of  Sprengel  and  of  Darwin  that 
color  attracts  insects  from  a  distance  is  rehabilitated. 

Andreae's  criticisms  of  Plateau's  work. — In  connection  with  Plateau's 
statement  that  we  have  no  means  of  knowing  that  the  perception  of  color 
by  insects  is  the  same  as  with  man,  Andreae  pointed  out  that  this  was 
equally  true  of  odor,  declaring  that  the  whole  question  was  an  idle  one  and 
that  the  only  thing  of  importance  was  to  determine  whether  what  we  call 
color  exerts  an  attractive  effect  upon  insects  or  not.  He  also  emphasized  the 
fact  that  many  of  Plateau's  experiments  were  excellent  in  demonstrating 
choice  among  colors,  but  they  had  no  value  for  the  question  of  the  relative 
merits  of  color  and  odor.  The  chief  error  in  his  investigations  lay  in  the 
fact  that  he  failed  at  the  outset  to  organize  his  queries  properly.  In  the 
first  place  all  possible  factors  that  bring  about  attraction  must  be  considered, 
and  in  the  second  as  many  of  these  as  possible  must  be  tested  at  the 
same  time.  In  this  way  alone  can  comparative  results  be  obtained  that 
will  lead  to  an  objective  conclusion  as  to  the  importance  of  form,  luster, 
brightness,  and  color,  honey-odor,  or  fragrance.  Many  of  Plateau's  results 
were  to  be  ascribed  to  the  effect  of  habit,  and  the  others  were  not  organized  to 
}deld  a  definite  decision  as  to  color  and  odor.  However,  Andreae's  state- 
ment that  the  greater  proportion  of  visits  to  the  decorollate  poppies  did 
not  change  the  essential  facts  with  respect  to  the  attraction  of  the  corolla 
does  not  seem  valid.  Finally,  it  was  stated  that  Plateau  had  not  sufficiently 
distinguished  the  behavior  of  various  insects  in  regard  to  color  and  odor, 
since  the  lower  apids  gave  results  directly  opposite  to  those  obtained  with 
the  higher  ones. 

Plateau's  criticisms  of  Andreae's  work. — Plateau  stated  (1906:13) 
that  it  was  probable  that  the  artificial  flowers  of  Andreae  and  of  Reeker 
would  have  exhibited  the  same  sources  of  error  as  those  employed  by  Wery 
(p.  185).  With  respect  to  the  experiments  with  Crocus  in  which  the  flowers 
were  covered,  it  was  objected  that  the  bees  upon  returning  to  the  habitual 


RELATED  STUDIES  AND  CRITIQUES.  183 

place  and  not  finding  the  flowers  precipitated  themselves  upon  the  imita- 
tion, as  upon  any  object  whatsoever.  The  same  objection  was  raised  to 
the  experiments  with  the  poppy,  the  results  of  which  were  regarded  as 
illusory  because  of  this  fact,  as  well  as  because  the  flowers  were  cut  off  and 
handled,  and  to  those  with  Dahlia.  The  experiments  with  Zinnia  were 
also  regarded  as  demonstrating  nothing  whatsoever,  since  the  artificial 
flowers  were  attached  to  the  stems  to  which  the  bees  were  accustomed  to 
come  to  visit  the  natural  ones.  Moreover,  it  was  supposed  that  the  meshes 
of  the  wire-gauze  were  so  small  that  the  odor  could  escape  little  if  at  all. 
Both  of  these  objections  were  also  urged  against  the  results  obtained  with 
Salvia  horminum,  but  their  validity  does  not  seem  to  be  great,  and  they 
can  not  apply  to  the  many  cases  in  which  the  artificial  flowers  were  placed 
at  distances  of  several  meters. 

Wery's  experiments   with   decorollate   and   artificial   flowers. — At 

the  suggestion  of  Errera  and  Massart,  and  under  their  supervision,  Wery 
(1904:1211)  made  a  series  of  investigations  to  determine  whether  color 
exerted  an  attraction  upon  insects  and  whether  this  was  greater  or  less  than 
that  due  to  odor.  An  interesting  historical  introduction  is  given,  but  no 
direct  criticism  of  Plateau's  work  is  made,  except  to  point  out  that  this 
investigator  modified  his  earlier  conclusions  as  to  odor  and  color  in  1899, 
and  in  1902  he  admitted  that  he  had  ascribed  an  exaggerated  importance 
to  odor.  The  first  experiments  with  decorollate  flowers  demonstrated  that 
different  insects  behaved  differently  in  response  to  color  and  odor,  the  higher 
bees,  Apis  and  Bombus,  visiting  the  normal  flowers  in  much  greater  number, 
Eristalis  showing  a  marked  but  slighter  preference,  and  the  flies  and  other 
small  Diptera  exhibiting  little  difference.  This  showed  that  it  was  not 
permissible  to  group  such  various  insects  together  in  studies  of  attraction 
and  consequently  the  visits  of  honey-bees  alone  were  taken  into  account 
in  these  experiments,  a  fact  that  explained  in  part  their  disagreement  with 
those  of  Plateau.  A  further  explanation  of  this  difference  was  afforded 
by  the  fact  that  the  bouquets  were  always  separated  by  a  distance  of  several 
meters  and  sufficiently  isolated  to  avoid  errors  due  to  any  other  attractive 
object.  Moreover,  the  flowers  were  changed  about  in  order  to  eliminate 
errors  arising  from  the  habits  of  the  bees.  The  experimental  area  was  stripped 
of  all  other  flowers  and  the  space  between  these  and  the  hive  was  cleared 
of  all  plants,  so  that  the  bees  flew  straight  from  the  hive  in  direct  response 
to  attraction  and  the  visits  were  not  the  result  of  hazard.  The  bouquets 
were  not  exposed  between  experiments  and  the  artificial  flowers  were  put 
away  to  make  sure  that  the  bees  would  not  ignore  them  in  consequence 
of  vain  visits.  An  endeavor  was  made  to  count  only  the  visits  of  bees  coming 
from  the  hive  or  from  a  distant  flight  during  which  they  had  gone  to  other 
flowers.  In  removing  the  corolla  care  was  taken  not  to  injure  the  nectaries 
and  great  care  was  also  given  to  following  the  precautions  laid  down  by 
Plateau,  such  as  washing  the  hands,  avoiding  the  use  of  perfume,  not  touch- 
ing the  flowers  with  the  hands  and  using  the  scissors  for  no  other  purpose. 
The  objection  of  Plateau  that  insects  would  not  visit  cut  flowers  was  not 
confirmed,  except  when  the  temperature  was  unfavorable,  as  at  other  times 
they  were  abundantly  visited  by  insects  of  diverse  species. 


184  PRINCIPLES  AND  CONCLUSIONS. 

The  first  experiments  were  carried  out  by  means  of  a  bouquet  each 
of  normal  and  decorollate  flowers  of  Epilobium  spicatum  and  Malva  silves- 
tris,  placed  10  meters  apart.  The  normal  flowers  of  these  received  respec- 
tively 14  and  4  visitors,  of  which  7  and  2  were  honey-bees,  while  the  muti- 
lated ones  yielded  12  and  3,  of  which  5  and  1  were  bees,  the  totals  for  the 
former  being  18  and  9,  and  for  the  latter  15  and  6.  When  Epilobium  and 
Antirrhinum  majus  were  employed,  there  were  19  visitors  to  the  intact 
and  13  to  the  mutilated  flowers,  the  number  of  bees  being  twice  as  great 
in  the  former.  Symphytum,  officinale  was  added  in  the  next  test,  which 
gave  27  visitors  to  normal  and  24  to  mutilated  flowers,  while  the  respec- 
tive numbers  for  the  bees  were  20  and  6.  The  next  installation  consisted 
of  two  bouquets  of  Centaurea  cyanus,  Papaver  rhoeas,  and  Pyrethrum  leucan- 
themum  separated  by  a  distance  of  25  meters  and  500  meters  from  two  hives. 
The  flowers  of  one  bouquet  were  left  intact,  while  the  petals  or  the  ray- 
flowers  were  cut  off  in  the  other.  The  former  received  43  visits,  29  of  them 
by  the  honey-bee,  and  the  latter  27,  of  which  10  were  made  by  the  bee.  The 
following  year  the  visits  of  the  honey-bee  alone  were  counted,  the  instal- 
lation comprising  two  bouquets,  one  intact,  the  other  decorollate,  which 
were  exchanged  after  each  series.  The  results  of  6  observations  gave  a 
total  of  72  bees  for  the  normal  flowers  to  28  for  the  mutilated  ones.  The 
total  for  the  two  years  was  respectively  138  and  46,  the  bees  being  much 
more  attracted  by  the  normal  flowers,  in  the  ratio  of  3: 1. 

When  a  dish  of  honey  was  placed  at  6  meters  from  a  bouquet  of  normal 
flowers,  the  latter  gave  49  visitors,  the  former  none,  while  the  totals  for 
two  further  observations  were  25  and  0.  When  a  bouquet  of  artificial 
flowers  of  Eschscholtzia  and  Dahlia  was  placed  6  meters  from  one  of  normal 
ones,  it  was  visited  by  15  bees,  to  17  for  the  latter,  the  visitors  scarcely 
landing  before  perceiving  their  error.  The  final  results  of  the  series  gave 
almost  equal  numbers,  showing  that  the  artificial  flowers  were  equally 
attractive.  Two  experiments  were  made  with  the  normal  bouquet  in  a 
closed  globe  in  order  to  suppress  the  perfume,  resulting  in  5  visitors  in 
contrast  to  6  for  the  artificial  one.  In  competition  with  a  bouquet  of 
natural  flowers  deprived  of  the  corolla,  the  artificial  flowers  received  11 
visitors  in  contrast  to  6.  Hiding  a  bouquet  of  normal  flowers  under  the 
foliage  resulted  in  but  7  visitors  to  it  in  comparison  with  32  to  a  similar  one 
freely  exposed.  In  a  check  with  artificial  flowers  entirely  visible  and  normal 
ones  hidden  in  the  foliage,  19  bees  went  to  the  first  and  but  4  to  the  last, 
demonstrating  that  odor  is  much  less  effective  than  color. 

The  remaining  experiments  made  use  of  honey  or  fragrant  flowers,  the 
installation  for  the  first  consisting  of  bouquets  of  normal  and  artificial 
flowers  fully  visible,  normal  flowers  hidden  under  leaves,  and  a  dish  of 
honey,  all  2  meters  apart.  The  respective  numbers  of  bees  were  25,  20, 
7,  and  1.  The  check,  which  differed  only  in  having  2  artificial  dahlias  stuck 
in  the  honey,  gave  respectively,  15,  11,  3,  and  8  bees,  the  dahlias  having 
greatly  increased  the  attractiveness  of  the  dish  with  honey.  When  yellow 
pollen  flowers  (Eschscholtzia)  were  placed  in  a  dish  of  honey  6  meters  away 
from  honey  alone,  no  bees  went  to  the  latter,  while  14  flew  directly  to  the 
flowers  and  for  the  most  part  to  the  stamens,  only  3  going  to  the  honey. 
A  bouquet  of  brilliant  flowers  with  little  odor  was  placed  6  meters  from 


RELATED  STUDIES  AND  CRITIQUES.  185 

another  containing  mignonette,  with  marked  perfume  and  dull  color;  the 
former  was  visited  by  35  bees,  the  latter  by  6.  When  the  bouquet  of  normal 
blossoms  was  replaced  by  one  of  artificial  flowers,  equally  brilliant,  the  figures 
were  25  and  6.  In  the  final  installation,  made  first  on  a  day  with  few  bees 
flying,  6  bees  went  to  a  dish  of  honey  to  which  natural  flowers  were  added, 
4  to  one  with  artificial  flowers,  and  none  to  honey  alone  or  with  green  leaves 
merely.  In  the  check,  the  dish  with  natural  flowers  gave  14  visitors,  that 
with  artificial  ones  15  visitors,  and  the  honey  with  leaves  or  honey  alone, 
none.  Finally,  the  author  endeavored  to  give  a  numerical  expression  to 
attraction  by  means  of  a  table  of  her  own  results,  as  well  as  one  for  those 
of  Andreae  and  Giltay.    The  conclusions  drawn  were  as  follows : 

1.  Flowers  provided  with  brightly  colored  parts  have  a  much  greater  attraction 

for  the  honey-bee  than  those  of  the  same  species  when  deprived  of  these  parts. 

2.  Honey  attracts  bees  very  little. 

3.  Under  the  conditions  given,  artificial  flowers  attracted  honey-bees  readily,  to  the 

same  degree  as  normal  flowers  placed  in  a  globe. 

4.  Perfume  alone  attracts  bees  but  feebly,  while  bright  color  and  form  taken  together, 

but  detached  from  odor,  exercise  a  very  manifest  attraction  upon  them. 

5.  From    the  juxtaposition  of  the  three  principal  factors,  form,  color,  and  odor, 

associated  in  the  memory,  results  the  most  marked  attraction. 

6.  For  the  honey-bee  the  attraction  exerted  by  the  form  and  color  of  flowers  is  approxi- 

mately four  times  greater  than  that  of  their  pollen,  perfume,  and  nectar  taken 
together.  Thus,  if  the  total  attraction  exerted  by  the  most  attractive  flowers 
is  taken  as  100,  that  of  form  and  color  will  be  represented  by  about  SO  and 
that  of  the  other  three  factors  by  about  20. 

Plateau's  criticisms  of  Wery's  experiments. — In  discussing  the 
discrepancy  between  his  results  and  those  of  Wery  and  Andreae  in  particular, 
Plateau  (1906:11)  thought  it  probable  that  this  was  due  to  certain  dis- 
turbing factors.  In  order  to  discover  these,  it  appeared  necessary  to 
secure  conclusive  evidence  as  to  the  nature  of  the  materials  employed  by 
his  opponents,  and  to  repeat  their  experiments  and  add  new  ones  surrounded 
by  all  possible  precautions.  A  preliminary  examination  showed  that  certain 
artificial  flowers  of  commerce  are  only  partly  artificial;  thus  the  yellow 
disk  of  oxeye  daisies  consisted  of  the  natural  receptacle  dried  and  dyed, 
the  involucre  of  the  cornflower  was  simply  the  natural  one  dried,  etc. 
Moreover,  the  stiffness  of  the  petals  in  artificial  flowers  for  hats  is  secured 
by  means  of  a  large  amount  of  starch  and  the  anthers  are  composed  of  balls 
of  paste,  which  are  eaten  by  small  Hymenoptera.  He  then  obtained  samples 
of  the  flowers  used  by  Wery  and  found  his  suspicions  to  be  confirmed.  In 
all  the  flowers  their  rigidity  was  due  to  the  presence  of  starch.  The  yellow 
color  of  Helianthus  and  Eschscholtzia  was  derived  from  a  saffron  dye  obtained 
from  the  stigmas  of  Crocus  sativus  and  containing  a  yellow  glucoside  ac- 
companied by  a  volatile  odor  attractive  at  least  to  certain  insects.  The 
disk  flowers  of  Dahlia  were  made  of  yellow  fibers,  some  of  which  were  covered 
with  gum  and  rolled  in  flour.  Balls  of  wheat  flour  colored  yellow  consti- 
tuted the  yellow  center  of  Aster,  and  the  anthers  of  Eschscholtzia  were 
made  of  similar  starchy  material  colored  blue  by  iodin.  Although  it  was 
not  supposed  that  the  presence  of  such  substances  explained  all  the  dif- 
ferences, it  was  thought  to  be  responsible  for  them  in  part.    Finally,  the 


186  PRINCIPLES  AND  CONCLUSIONS. 

artificial  flowers  used  by  Miss  Wery  were  regarded  as  imitations  of  very 
mediocre  value. 

In  the  experiments  where  Dahlia  was  used,  Plateau  stated  that  the 
figures  probably  did  not  really  indicate  that  the  artificial  flowers  were 
practically  as  attractive  as  the  natural  ones,  for  three  reasons.  The  first 
was  the  error  committed  in  carrying  out  these  tests  where  a  series  of  8 
experiments  with  bouquets  had  been  made  during  the  preceding  two  weeks, 
giving  an  opportunity  for  the  exercise  of  place-memory  by  the  bees.  The 
second  was  the  fact  that  the  majority  of  the  insects  barely  landed  on  the 
artificial  flowers,  these  visits  to  be  interpreted  rather  as  hesitations,  curves, 
or  crochets  made  in  flight,  and  the  third  dealt  with  the  materials  used  in 
the  artificial  flowers. 

Experiments  of  Weismann  and  Errera. — Weismann  (1902:219) 
placed  an  artificial  Chrysanthemum  in  the  midst  of  normal  flowers  actively 
visited  by  butterflies.  He  found  that  most  of  the  latter  passed  near  the 
imitation  without  stopping,  but  he  saw  two  alight  on  it  and  probe  actively 
with  the  ligule  before  flying  away.  It  seemed  evident  that  they  sought  the 
nectar  which  they  had  found  in  the  normal  flowers  and  that  they  flew  off 
only  after  having  determined  its  absence.  Errera  (Wery,  1904:1224) 
placed  two  bouquets  made  up  of  the  same  number  of  flowers  of  the  same 
species  in  similar  vases  at  a  considerable  distance  from  each  other  in  the 
midst  of  an  extensive  greensward  at  Brussels.  In  one  the  flowers  were 
normal,  in  the  other  they  were  deprived  of  their  corollas  in  such  a  way  as 
not  to  injure  the  nectaries.  The  decorollate  bouquet  was  still  rather  con- 
spicuous, owing  to  the  colored  stamens  of  Rhododendron,  the  white  calyx 
of  Hesperis,  and  the  yellow  disks  of  Chrysanthemum.  The  two  bouquets 
were  visited  at  the  rate  of  46  per  hour  for  the  normal  and  24  for  the  de- 
corollate, the  majority  of  the  visitors  being  flies. 

Orientation  of  the  honey-bee  at  flowers  of  the  same  species. — 

Detto  (1905:424)  carried  out  a  number  of  experiments  to  determine  the 
relative  importance  of  color  and  odor  in  the  attraction  of  the  honey-bee, 
as  well  as  to  throw  light  upon  the  rapidity  with  which  it  learned.  The 
first  series  dealt  with  the  manner  in  which  the  bee  is  led  from  one  flower  to 
another  of  the  same  plant  or  different  plants  of  the  same  species.  When 
flowers  were  mutilated  by  removing  the  anther  mass  or  half  the  corolla,  they 
were  visited  like  the  normal  ones,  but  when  the  corolla  was  completely  sup- 
pressed, visits  ceased  immediately,  to  begin  again  as  soon  as  it  was  replaced. 
Visits  also  stopped  at  once  as  soon  as  the  corolla  was  replaced  by  one  of 
yellow  tissue-paper,  but  were  resumed  when  the  normal  corolla  was  put  in 
position  again.  Shortening  the  corolla  to  a  third  did  not  affect  its  attraction, 
and  finally,  after  a  few  hours  the  decorollate  flowers  began  to  receive  visitors, 
but  in  a  smaller  degree  than  the  normal  ones.  These  tests  show  how  im- 
portant a  guide  the  colored  corolla  is  in  the  near-flight  of  habituated  honey- 
bees, and  the  visits  to  decorollate  flowers  merely  prove  that  they  are  able 
to  form  new  associations  in  consequence  of  the  stimulus  afforded  by  the 
abundant  nectar.  If  flowers  with  excised  anther  column  were  provided 
with  a  colored  paper  disk  with  a  hole  in  the  center,  thus  cutting  off  the 
lower  third  of  the  flower,  part  of  the  bees  avoided  such  flowers  and  others 


RELATED  STUDIES  AND  CRITIQUES.  187 

alighted  for  but  a  moment.  Many,  however,  rushed  about  on  the  disk 
and  some  succeeded  in  passing  under  the  edge  or  through  the  opening  to 
the  nectaries.  In  three  other  flowers  the  anther  column  was  replaced  by  a 
staminate  flower  of  Bryonia  and  the  results  were  similar,  some  bees  shunning 
the  artefacts  and  others  succeeding  after  persistent  endeavor  in  finding 
the  nectar.  It  was  concluded  that  in  Anoda  triloba  the  colored  corolla  is 
the  guide  in  the  flight  from  flower  to  flower  and  that  near-flight  is  deter- 
mined by  optical  orientation  to  color. 

In  the  case  of  Bryonia  dioeca,  flowers  provided  with  a  ring  of  colored 
paper  were  readily  visited,  the  visits  to  the  different  colors  being,  yellow  12, 
blue  8,  green  6,  and  red  1.  When  the  anthers  were  concealed  by  colored 
disks,  the  visits  were  fewer  than  to  normal  flowers,  yellow  again  leading, 
and  visits  continued  at  about  the  same  rate  when  the  anthers  were  excised. 
The  complete  removal  of  the  perianth  greatly  decreased  the  number  of 
visits.  The  conical  disk  of  three  heads  of  Rudbeckia  laciniata  was  covered 
with  a  thin  glass  tube,  with  the  result  that  numerous  bees  flew  against 
the  glass,  some  crawling  all  over  it  and  others  flying  about  it  several  times. 
In  two  heads  the  cone  was  replaced  by  the  similar  one  of  Heliopsis  levis; 
some  bees  hovered  over  this  and  others  crawled  about  on  it,  but  none 
sipped  nectar  from  it.  Heads  of  Echinacea  purpurea  placed  between  those 
of  Rudbeckia  were  not  visited,  but  they  were  sought  when  the  disk  was 
replaced  by  that  of  Rudbeckia.  In  order  to  determine  the  effect  of  the  yel- 
low ray-flowers,  the  cones  of  two  heads  were  completely  removed;  bees 
coming  from  higher  heads  or  those  on  the  same  level  paid  little  attention 
to  these,  but  those  coming  from  below  alighted  on  them  for  a  moment  or 
darted  over  the  middle.  When  the  disk  was  covered  with  blue  or  yellow 
paper,  bees  arriving  on  the  same  level  or  from  below  alighted  on  the  paper 
before  perceiving  their  mistake.  Bees  coming  from  above  visited  the  green 
disk  after  the  ray-flowers  had  been  covered  with  colored  paper,  but  the 
visits  decreased  in  cases  where  the  rays  were  all  removed.  These  results 
were  considered  to  prove  that  visits  are  determined  by  optical  signals, 
and  that  either  ray-flowers  or  disk  suffice  for  attraction,  though  the  green 
disk  is  naturally  less  effective  in  this  respect. 

From  this  series  of  experiments  it  was  concluded  that  the  colored  corolla 
is  the  normal  guide  to  the  individual  flowers  of  a  cluster  or  group,  but  other 
guides  may  be  utilized  with  the  result  that  decorollate  flowers  may  continue 
to  be  visited.  In  consequence  no  conclusion  as  to  the  absence  of  the  color- 
sense  can  be  drawn  from  habituated  bees.  The  means  of  orientation  in  the 
flight  from  flower  to  flower  is  optical  in  nature.  Since  the  different  at- 
tractive parts  of  the  flower  can  bring  about  visits  when  present  alone,  it 
is  easily  seen  that  partly  concealed  flowers  may  be  visited.  This  also  ex- 
plains why  the  differently  colored  varieties  of  a  species  are  visited  indif- 
ferently by  bees ;  this  is  possible  whenever  the  flowers  agree  in  the  possession 
of  one  important  guide  for  the  insects,  which  may  be  some  other  part  than 
the  corolla. 

Discrimination  between  similar  species  of  flowers. — In  further 
studies  Detto  placed  clusters  of  Deutzia  flowers  in  umbels  of  Crataegus. 
The  bees  behaved  differently  on  them,  some  sipping  nectai ,  others  not,  but 
they  all  flew  or  crawled  to  the  neighboring  flowers  of  Crataegus.     When 


188  PRINCIPLES  AND  CONCLUSIONS. 

umbels  of  Crataegus  were  placed  between  clusters  of  Deutzia,  the  behavior 
was  the  reverse.  A  similar  discrimination  was  found  in  the  case  of  heads 
of  Rudbeckia  provided  with  disks  from  Heliopsis,  and  these  results  led  to 
the  conclusion  that  flowers  of  similar  color  are  distinguished  on  near 
approach  by  means  of  the  odor  of  the  nectar  or  the  flower  itself.  The  ap- 
proach of  bees  habituated  to  a  particular  species  to  the  flowers  of  a  similar 
species  intermingled  with  it  attests  their  color-sense,  since  they  perceive  the 
difference  only  in  the  immediate  vicinity  of  each,  through  the  perception 
of  the  strange  odor.  Detto  considered  it  unwarranted  to  ascribe  this 
ability  to  discriminate  to  the  perception  of  form,  as  was  done  by  Forel, 
Buttel-Reepen,  and  Knuth,  but  this  conclusion  is  contradicted  by  his 
earlier  statement  that  pistil  and  anthers  serve  as  guides  in  decorollate 
flowers.  He  called  attention  to  the  conflict  between  the  views  of  Knuth 
and  Andreae  as  to  the  attraction  sequence  of  color  and  odor,  and  agreed 
with  the  latter  that  far -flight  in  the  case  of  newcomers  is  due  to  color  and 
near-flight  to  odor,  though  this  was  not  true  of  all  groups  of  insects. 

Orientation  of  the  bee  within  the  flower. — In  order  to  determine 
whether  bees  are  guided  by  vision  or  smell  in  going  from  one  nectary  to 
another,  Detto  made  use  of  flowers  of  Althea  rosea,  in  which  the  deep  comate 
nectaries  are  about  9  mm.  apart.  Honey-bees  and  bumble-bees  go  from  one 
nectary  to  the  next  with  the  greatest  accuracy,  without  feeling  with  the  an- 
tennae or  probing  with  the  ligule.  The  anther  column  was  removed  and  a 
paper  disk  put  in  place  in  such  a  manner  that  it  covered  the  nectaries ;  it  was 
perforated  in  a  way  to  permit  the  nectaries  to  be  closed  or  opened  by  a  turn. 
Some  bees  avoided  such  flowers,  while  others  entered  and  quickly  found  the 
nectar  through  the  openings,  going  to  them  all  in  normal  fashion.  As  one 
bee  went  from  the  first  to  the  second  nectary,  the  disk  was  turned  to 
bring  the  openings  between  the  nectaries;  he  went  to  the  next  perforation. 
In  repeated  trials,  some  of  the  insects  flew  away  after  the  first  futile  attempt, 
others  went  to  several  openings,  and  still  others  kept  probing  until  they 
were  able  to  reach  the  nectar  by  oblique  movements  of  the  ligule.  Finally, 
some  forced  up  the  edge  of  the  disk  and  crawled  beneath  it.  When  the  disk 
had  no  perforations,  the  bees  sought  to  force  the  head  under  the  edge  at 
all  points  and  not  merely  in  the  direction  of  the  nectaries.  With  holes  1  mm. 
in  diameter  directly  above  the  nectaries,  the  bees  made  no  attempt  to  reach 
the  nectar.  While  these  results  were  not  regarded  as  entirely  conclusive, 
they  seemed  to  indicate  that  vision  was  the  decisive  factor  in  directing  the 
insect  to  each  nectary.  An  ingenious  check  was  constructed  by  cutting  out 
a  disk  from  a  hollyhock  flower  in  such  a  manner  that  the  nectaries  were  with- 
out a  bottom  and  could  be  brought  above  or  between  the  nectaries  of  a 
normal  flower  at  will.  As  a  further  precaution  the  false  nectaries  were 
thoroughly  washed  out  to  free  them  of  odor  in  so  far  as  possible.  When 
the  false  nectaries  were  directly  above  the  true  ones,  the  bees  visited  the 
latter  in  the  normal  way,  but  when  they  were  brought  into  the  intervals 
the  bees  continued  to  go  to  the  false  nectaries  without  success.  Although 
it  was  impossible  to  be  certain  that  the  latter  were  entirely  without  odor, 
it  seems  highly  probable  that  the  nectar  journey  is  controlled  by  vision. 
If  odor  be  regarded  as  chiefly  directive,  it  must  be  assumed  that  its  inten- 
sity decreases  with  the  distance  from  each  nectary,  as  otherwise  the  bee 


RELATED  STUDIES  AND  CRITIQUES.  189 

could  not  go  directly  to  each  one.  However,  several  facts  argue  against  this 
assumption.  The  bees  behave  in  the  normal  manner  even  when  the  flowers 
sway  back  and  forth  in  a  strong  wind.  Spraying  menthol  in  the  nectaries 
does  not  change  the  behavior,  except  that  the  bees  fly  away  after  probing 
such  a  nectary  or  go  rapidly  to  the  next.  Moreover,  the  layering  and  the 
concentration  of  the  nectar  odor  above  the  nectaries  must  be  obliterated 
by  its  mixing  with  the  odor  of  the  flower  itself. 

Detto  also  gave  an  interesting  account  of  the  training  of  an  individual 
bee,  which  was  effected  by  covering  a  flower  cluster  with  glass.  The  cluster 
was  thus  changed  by  the  addition  of  the  glass,  the  greater  accumulation 
of  nectar  in  consequence  of  fewer  visits,  and  a  corresponding  increase  of 
fragrance.  The  abundance  of  nectar  appeared  to  be  the  chief  factor  in  the 
association  through  which  the  bee  gradually  accustomed  itself  to  the  new 
marks  of  the  cluster  and  finally  came  to  gather  nectar  from  it  almost 
exclusively,  so  that  it  might  be  said  to  know  it. 

The  following  general  statements  were  made  with  respect  to  the  sigifi- 
cance  of  color  in  the  attraction  of  bees: 

1.  The  assumption  of  Sprengel,  Darwin,  Mueller,  Buttel-Reepen,  and  others  that  the 

color  of  the  flower  brings  about  the  attraction  of  the  higher  bees,  Apis  and 
Bombus,  has  been  established  by  the  investigations  of  Forel,  Andreae,  and 
Giltay. 

2.  However,  since  flowers  'with  inconspicuous  corollas  are  often  abundantly  visited 

by  honey-bees  and  bumble-bees  (Ampelopsis,  Vitis,  Rhamnus  frangula,  Coton- 
easter  acutifolius,  etc.,  with  greenish  flowers),  the  bright  color  of  corolla  or 
inflorescence  is  not  an  indispensable  condition.  Still,  color  must  play  a  sig- 
nificant part  in  the  competition  of  species  for  the  visits  of  the  most  dependable 
pollinators,  since  striking  colors  are  more  easily  found  than  dull  ones  and  since 
these  insects  orient  themselves  in  flight  exclusively  with  their  eyes  (Buttel- 
Reepen,  Forel). 

3.  The  return  of  a  habituated  bee  to  the  plant  is  independent  of  the  color  signal, 

probably  indeed  after  the  first  visit,  since  the  bees  are  able  to  refind  the  place 
of  the  desired  plant  through  optical  orientation  to  the  surroundings  (Buttel- 
Reepen,  Giltay,  etc.). 

4.  Guidance  to  the  individual  flowers  of  an  inflorescence  takes  place  by  means  of 

vision.  Normally  the  color  of  the  corolla  is  the  chief  factor  in  guiding  the  bees 
to  the  single  flowers.  Sometimes  other  features  of  the  flower  have  a  share  in 
this,  and  the  removal  of  the  corolla  does  not  necessarily  cause  a  cessation  of 
visits. 

5.  The  distinction  of  flowers  of  the  same  color  but  different  species  by  the  honey-bee 

is  very  probably  due  to  the  perception  of  odor  when  near  at  hand. 

6.  It  is  very  probable  that  honey-bees  and  bumble-bees  locate  the  nectaries  of  large 

flowers  by  means  of  vision. 

Chance  observation  of  visits  to  imitations. — Plateau  (1906:148) 
has  collected  the  records  of  the  great  majority  of  accidental  observations  of 
visits  to  artificial  flowers  on  hats,  flower  designs  on  tapestry  or  wall-paper, 
and  bits  of  colored  paper  or  cloth.  To  these  a  few  others  are  added  here  to 
make  the  record  complete  and  to  permit  a  discussion  of  their  significance  in 
the  light  of  Plateau's  criticisms.  The  first  recorded  instance  of  such  visits 
appears  to  have  beeen  made  by  Houzeau  (1872:132),  who  stated  that 
Trevillian  saw  an  individual  of  Sphinx  convoluta  fly  along  wall-paper  orna- 


190  PRINCIPLES   AND   CONCLUSIONS. 

merited  with  brilliant  flowers  and  try  to  probe  the  fanciful  corollas.  A 
similar  observation  by  Vallete  (1875)  had  the  fortunate  consequence  of 
stimulating  Plateau  to  undertake  his  first  experiments,  as  already  indicated 
(p.  136),  and  this  was  followed  by  another  one  made  on  artificial  flowers: 

"After  the  experiments  of  Plateau,  I  watched  for  an  opportunity  to  renew  my 
observations,  the  occasion  for  this  presenting  itself  while  I  was  at  La  Roche-sur-Yon 
last  October.  An  individual  of  Macroglossa  stellatarum  entered  the  room  and  per- 
ceiving two  baskets  of  artificial  flowers,  roses,  violets  and  others,  that  decorated  the 
mantel-piece,  flew  precipitately  toward  them.  But  I  must  confess  that  he  had  barely 
unrolled  the  ligule  before  the  baskets  when  he  flew  away.  He  had  recognized  his 
error,  or  at  least  this  seems  to  be  the  explanation  to  be  given.  Led  into  error  by  the 
sense  of  sight,  the  mistake  was  rectified  by  means  of  the  sense  of  smell"  (1878). 

Burton  recorded  a  corresponding  observation  the  same  year  (1878:162): 

"In  going  by  steamboat  from  Como  to  Maggiore  in  September,  1875,  I  saw  a 
Macroglossa  stellatarum  dart  towards  some  brightly  colored  flowers  in  a  lady's  hat, 
hover  a  short  time  above  them,  and  then  fly  away.  It  remained  long  enough  to  con- 
vince me  that  it  had  examined  the  flowers  and  had  recognized  its  error." 

In  a  discussion  of  the  mistakes  made  by  animals,  Romanes  (1884:167) 
cited  the  following  cases: 

"Again,  the  Rev.  Mr.  Bevan  and  Miss  C.  Shuttleworth  write  me  independently 
that  they  have  seen  wasps  and  bees  visiting  representations  of  flowers  upon  the  wall- 
paper of  rooms  and  Trevillian  saw  the  same  mistake  made  by  a  sphinx-moth.  Swainson 
in  his  'Zoological  Illustrations'  gives  an  analogous  case  in  a  vertebrated  animal; 
an  Australian  parrot,  whose  food  is  taken  from  the  flowers  of  the  Eucalyptus,  was 
observed  endeavoring  to  feed  on  the  representations  of  flowers  on  a  cotton-print  dress. 
Likewise,  Professor  Moseley,  F.  R.  S.,  informs  me  that  he  has  noticed  honey-seeking 
insects  mistake  for  flowers  the  bright-colored  salmon  flies  stuck  in  his  hat  while  fishing, 
and  Mr.  F.  M.  Burton,  writing  to  Nature,  says  that  he  has  observed  the  humming- 
bird hawk-moth  (Macroglossa  steUatarum)  mistake  artificial  flowers  in  a  lady's  hat 
for  real  ones.  Still  more  curiously,  the  naturalist  Couch  observed  a  bee  mistake 
a  sea-anemone  (Tealia  crassicomis) ,  which  was  'covered  merely  by  a  rim  of  water,' 
for  a  flower,  darting  to  the  center  of  the  disk,  'and  though  it  struggled  a  good  deal 
to  get  free,  was  retained  till  it  was  drowned  and  was  then  swallowed."' 

Blanchard  (1891),  upon  entering  a  hotel  room  in  Adelsberg  in  September, 
1890,  found  a  sphinx- moth  fluttering  about,  apparently  deceived  by  the 
seeming  twilight.  It  successively  examined  each  of  the  flowers,  painted 
in  blue,  violet,  yellow,  and  dull  red,  that  formed  the  cluster  at  the  center 
of  the  ceiling.  The  proboscis  was  extended,  as  though  it  were  dealing 
with  real  flowers.  Disappointed  by  a  lack  of  success,  it  left  the  ceiling  to 
explore,  one  after  another,  a  large  number  of  the  yellowish  flowers  crudely 
figured  on  the  wall.  It  then  went  back  to  the  ceiling,  but  visited  only  a 
few  flowers  to  make  sure  that  it  was  not  deceived  the  first  time,  and  then 
returned  to  the  wall.  After  a  number  of  fruitless  visits  to  the  flowers  here, 
it  sought  refuge  in  the  hangings.  Blanchard  also  reported  a  statement 
of  Alphonse  DeCandolle  to  the  effect  that  he  had  frequently  seen  sphinx- 
moths  dart  to  the  flowers  found  on  wall-paper. 

The  studies  of  J.  Pe>ez  on  Macroglossa  led  to  those  of  Plateau  on  the 
same  insect,  which  were  designed  to  correct  the  impression  that  this  was 
due  to  an  actual  attraction  by  color.  An  earlier  observation  by  his  brother, 
B.  Perez,  was  reported  as  follows: 


RELATED  STUDIES  AND  CRITIQUES.  191 

"A  diurnal  sphinx  (Macroglossa  stellatarum)  entered  my  room,  in  which  there  is  a 
tapestry  with  a  clear  background  strewn  with  bouquets  of  white  and  rose  flowers 
with  green  stems  and  leaves.  For  two  minutes  the  insect  flew  from  bouquet  to 
bouquet,  stopping  before  5  of  them  with  the  ligule  unrolled  as  if  visiting  real  flowers. 
Afterwards  he  disappeared  suddenly,  possibly  because  I  moved  in  the  hope  of  observing 
him  more  closely." 

P£rez  himself  saw  an  individual  of  this  same  species  fly  abruptly  from  a 
pot  of  flowers  in  a  window  to  a  small  piece  of  rose-colored  paper  on  the 
pavement,  but  the  mistake  once  recognized  the  moth  disappeared  like  a 
flash  (1894).  Several  years  later  (1897),  he  stated  that  he  had  frequently 
deceived  this  moth  by  placing  bits  of  bright-colored  paper  on  shrubs,  and 
that  Eristalis  also  exhibited  a  similar  response. 

Lesne  (1895)  saw  a  fly  of  the  genus  Bombylius  alight  without  hesitation 
on  an  artificial  violet  of  his  sister's  hat  and  insert  the  ligule  in  the  corolla. 
Not  finding  nectar,  it  passed  at  once  to  a  second  and  then  to  a  third  in  the 
same  manner  before  flying  away  a  few  paces  to  rub  its  tongue  as  though  it 
had  been  roughly  treated.  It  was  concluded  that  smell  in  the  case  of  the 
Bombylidae  does  not  play  the  role  ordinarily  assumed,  but  that  vision  alone 
enables  them  to  discover  the  flowers  that  provide  their  food.  However, 
this  was  not  intended  in  an  absolute  sense,  since  it  was  later  stated  that  the 
bee-flies  are  guided  by  both  senses  acting  together  in  most  cases.  This 
discrepancy  was  pointed  out  by  Gazagnaire  (1895)  in  the  paper  immediately 
following,  and  it  was  contended  that  either  or  both  senses  acting  together 
could  enable  these  flies  to  distinguish  the  flowers  sought  and  that  errors 
would  be  frequent  only  when  they  were  flying  indifferently  and  not  in 
need  of  food.  Schnabl  (1896)  related  an  experience  of  Schuch,  who  saw 
a  Macroglossa  flying  before  a  tapestry  in  a  hotel  room,  on  which  were 
represented  flowers  of  Tropaeolum  majus.  It  went  to  the  flowers  from  time 
to  time  in  the  endeavor  to  plunge  its  ligule  into  the  corolla. 

Bedford  (1897),  while  walking  down  a  street  in  London,  noted  a 
butterfly  (Pieris  brassicae)  following  a  lady's  hat,  which  was  ornamented 
with  artificial  lilies  of  the  valley.  It  made  repeated  attempts  to  light  on 
the  flowers,  but  was  prevented  by  the  abrupt  movements  of  the  wearer 
and  finally  gave  up  the  endeavor.  Parkin  (1897)  related  the  observations  of 
his  friend  Winstaley  with  respect  to  a  honey-bee  that  entered  his  room. 
This  flew  at  first  to  some  paintings  on  the  wall  opposite  the  window, 
passed  from  one  to  the  other  in  making  the  round  of  the  room,  stopping 
for  an  instant  before  those  with  color,  and  then  disappeared  through  the 
open  door.  It  returned  and  flew  to  the  gas-globes,  returned  to  the  paint- 
ings, went  again  to  the  globes,  visited  four  glass  objects  on  the  mantel- 
piece, and  finally,  after  five  minutes  in  all,  departed  through  the  window. 
Thornley  (1897),  on  one  or  two  occasions  when  driving  a  pony  whose 
head  was  decorated  with  blue  rosettes,  saw  a  Macroglossa  fly  straight  to 
one  of  the  rosettes  and  hover  above  it  for  several  seconds,  although  the 
pony  had  begun  to  trot. 

Knuth  (18982)  recorded  the  case  of  Syrphus  that  flew  to  the  flowers  on 
his  wife's  hat  in  a  railway  station  at  Leipsic.  The  flowers  were  greenish- 
brown  with  a  velvet  sheen,  but  in  spite  of  their  inconspicuous  character 
and  lack  of  fragrance,  the  fly  hovered  over  them  for  several  minutes,  per- 


192  PRINCIPLES   AND   CONCLUSIONS. 

forming  its  characteristic  evolutions.  Gorka  (1898)  noted  two  individuals 
of  Deiliphila  elpenor  that  flew  along  the  walls  of  a  pavilion  painted  with 
crude  flowers  of  Phlox  and  Verbena  and  attempted  to  plunge  the  proboscis 
in  the  corollas.  Lack  of  success  did  not  discourage  them,  for  they  returned 
after  a  moment  to  renew  the  attempt.  In  the  instance  cited  by  Motelay 
(1898),  a  cabbage  butterfly  fluttered  against  the  window  of  a  florist's  shop, 
trying  for  10  or  15  minutes  at  all  parts  of  the  pane  to  reach  the  flowers 
on  the  inside.  It  appeared  certain  that  it  was  attracted  by  vision  and  not 
by  smell,  since  the  door  of  the  shop  was  open  but  6  or  8  feet  away,  and 
especially  since  the  butterfly  passed  the  door  as  it  flew  away.  Benary 
(1900)  stated  that  a  bumble-bee,  which  entered  a  room  through  the  open 
door,  flew  at  first  to  some  natural  flowers.  After  it  had  examined  all  of 
these,  it  sought  for  nearly  a  minute  to  insert  the  ligule  in  one  of  the  flowers 
of  the  carpet.  According  to  Aigner-Abafi  (1900),  Langhoffer  saw  a  bee  fly 
through  the  open  window  of  his  lecture-room  and  go  directly  to  a  colored 
botanical  wall-chart.  It  flew  to  one  cluster,  working  upward  and  then  to 
another  flower,  but  finding  itself  again  deceived  it  flew  away. 

Charlier  observed  that  the  males  of  Rhodocera  rhamni  were  greatly  at- 
tracted by  a  piece  of  green  paper  10  by  20  cm.  moving  gently  in  the  sun- 
shine. They  alighted  on  it  several  times  and  moved  about  in  an  agitated 
manner.  Errera  noticed  a  number  of  Hymenoptera  flying  about  the  hat 
of  a  country-woman  for  fully  a  half-hour.  The  hat  was  trimmed  with 
artificial  flowers,  full-blown  yellow  roses  and  pansies,  but  the  bees  flew  to 
the  former  and  neglected  the  latter.  They  were  so  numerous  and  their 
behavior  so  striking  that  it  was  remarked  by  several  people.  He  also 
reported  an  observation  communicated  by  Strasburger,  who  saw  Macro- 
glossa  stellatarum  light  on  the  red  oleander  flowers  of  the  wall-paper  of  a 
room;  the  hawk-moth  sought  to  visit  the  flowers  one  by  one  exactly  as 
though  they  were  natural  (Wery,  1904:1224,  1226).  Van  Bembeke,  while 
walking  in  a  park  at  Ghent,  saw  a  cabbage  butterfly  dart  toward  a  piece 
of  red  paper,  light  on  it  for  an  instant  and  then  depart  abruptly  (Wery,  1.  c). 

In  supporting  his  opinion  that  these  isolated  observations  were  without 
value,  Plateau  cited  the  case  of  a  Rhodocera  that  appeared  to  follow  a 
bicyclist  in  a  dark  costume,  who  was  mounted  on  a  wheel  without  bright 
colors,  pointing  out  that  the  presence  of  bright  colors  would  have  led  to  the 
fallacious  assumption  of  a  real  attraction.  Instances  of  visits  to  bits  of 
paper  were  regarded  as  fortuitous  and  without  significance,  and  it  was  em- 
phasized that  butterflies  often  light  on  objects  having  neither  the  form  nor 
the  color  of  flowers,  but  provided  with  an  odor.  With  respect  to  attraction 
by  the  colored  designs  of  wall-paper  or  tapestry,  he  remarked  that  several  of 
the  accounts  were  given  at  second-hand  and  that  some  of  these  were  merely 
verbal,  while  as  to  those  given  by  the  observer  himself,  the  latter  was  often 
taken  bj^  surprise.  This  fact,  together  with  the  poor  light  and  the  rapid 
movements  of  the  insects,  made  it  probable  that  the  findings  would  be 
very  different  from  those  of  an  investigator  prepared  to  follow  the  insect's 
behavior.  Moreover,  Macroglossa  and  other  insects  were  found  to  fly 
along  vertical  walls  without  flower  designs,  the  extension  of  the  ligule 
being  without  significance,  since  Breyer  stated  that  this  moth  and  the 
sphinx-moths  always  fly  with  the  ligule  unrolled.     Furthermore,  if  paint- 


RECENT   INVESTIGATIONS.  193 

ings  of  flowers  were  to  attract  insects,  colored  posters  bearing  flowers 
should  do  this  in  an  evident  degree,  which  is  obviously  not  the  case.  Finally, 
Plateau  gave  a  list  of  eight  objects,  mostly  dull  in  color,  on  which  a  bumble- 
bee alighted  in  his  study.  Likewise,  as  to  attraction  by  the  artificial  flowers 
of  hats,  he  regarded  the  cases  as  too  isolated  to  be  of  value,  those  of  an 
actual  attraction  being  explained  by  the  presence  of  some  dye  possessing 
an  odor  evident  at  least  to  certain  insects. 

Knoll's  critique  of  Plateau's  study  of  Macroglossa. — Knoll  (1922: 
363)  points  out  that  Plateau's  failure  to  interpret  the  behavior  of  Macro- 
glossa properly  was  due  largely  to  not  recognizing  that  the  "darkness 
flight"  of  the  hawk-moth  is  a  peculiar  response  of  this  insect.  He  was 
also  in  error  in  thinking  that  the  hawk-moth  always  flies  with  the  ligule 
unrolled,  and  was  thus  not  in  position  to  observe  the  finer  details  of  its 
behavior.  As  Perez  contended  earlier,  the  pieces  of  cloth  and  paper  used 
by  Plateau  were  too  large,  as  were  also  his  artificial  flowers.  Moreover,  the 
colored  objects  often  belonged  to  a  different  optical  group  from  the  flower 
visited  shortly  before  by  the  hawk-moth,  so  that  the  latter  had  no  predi- 
lection for  them,  contrary  to  the  case  when  the  color  group  was  the  same. 
Since  the  depth  of  color  plays  an  important  part,  it  is  not  strange  that  the 
few  moths  observed  by  Plateau  did  not  notice  the  artificial  objects  in 
which  the  color  was  less  saturated  than  in  the  flowers.  This  was 
especially  true  in  the  experiments  with  Anchusa  italica,  owing  to  its  remark- 
able deep-blue  color.  Finally,  Plateau's  arrangement  of  his  test  objects  was 
not  a  happy  one.  It  has  proved  undesirable  to  place  artificial  objects  in 
competition  with  large  plants  in  full  bloom,  as  the  insects  fly  directly  to 
the  latter  and  visit  the  artefacts  only  by  chance,  and  much  better  results 
have  been  secured  by  intermingling  the  test  objects  and  plants  with  few 
flowers.  The  same  effect  can  be  obtained  by  removing  the  flowers  in 
part  or,  better  still,  by  installing  a  path  of  flight  in  which  the  artefacts 
are  placed. 

With  respect  to  the  vexillary  role  of  the  bracts  of  Salvia  horminum,  Knoll 
remarks  that  the  visits  of  three  out  of  six  hawk-moths  to  such  clusters 
constituted  a  positive  result  and  not  an  error,  and  that  this  is  to  be  explained 
by  the  fact  that  Dianthus  and  Salvia  belong  to  the  same  color  group.  He 
also  found  these  colored  bracts  without  honey  to  be  sought  by  the  moths 
in  just  the  same  manner  as  the  usual  violet  honey  containers  and  a  similar 
response  was  obtained  in  nature.  He  concludes  that  the  bracts  greatly 
increase  visibility  at  a  distance  and  hence  possess  a  definite  vexillary  func- 
tion, contrary  to  the  views  of  Plateau  (cf.  Frisch,  1914:4,  1919:3). 

RECENT  INVESTIGATIONS. 
The  color  sense  of  the  honey-bee. — Lovell  was  the  first  to  carry  out 
extensive  experiments  on  pollination  in  America,  in  which  he  had  the  un- 
usual advantage  of  bringing  to  the  problem  the  experience  gained  by 
years  of  observation  in  this  field.  The  first  three  papers  of  the  series  deal 
with  the  color  sense  of  the  honey-bee,  the  fourth  with  conspicuous  flowers 
rarely  visited,  and  the  fifth  with  constancy.  As  indicated  in  the  first  (1909: 
338),  his  investigations  were  stimulated  by  Plateau's  conclusions  that  color 
and  form  are  unimportant  and  odor  alone  attractive  to  pollinators.    In 


194  PRINCIPLES  AND   CONCLUSIONS. 

order  to  determine  whether  conspicuousness  is  an  advantage  to  flowers, 
the  petals  were  removed  from  a  cluster  of  7  blossoms  of  Pirus  communis, 
which  had  received  8  visits  in  15  minutes.  No  visits  were  paid  to  it  in  the 
first  15  minutes  after  this,  and  but  2  in  the  second.  When  the  petals  were 
removed  from  one  of  two  adjacent  clusters  of  8  flowers,  the  normal  received 
11  visits  in  the  15-minute  period  to  none  for  the  mutilated  one.  Two  groups 
of  flowers  of  Borago  officinalis  6  inches  apart  received  15  and  13  visits 
in  10  minutes;  after  the  corolla  and  anthers  were  removed  from  one, 
no  bees  came  to  it,  while  the  normal  yielded  7  visits.  Although  bees  did 
not  go  to  the  decorollate  flowers,  they  twice  flew  to  withered  corollas  on 
the  ground.  In  the  case  of  a  staminate  flower  of  Cucurbita  maxima,  12 
visits  were  made  in  10  minutes,  4  of  them  by  Bombus  terricola.  The  removal 
of  the  perianth  decreased  the  number  of  visits  for  the  unit  period  to  a  single 
one  made  by  a  bumble-bee,  although  a  flower  wilted  and  nearly  closed 
received  5  visits.  Two  staminate  flowers  with  their  corollas  touching  were 
used  in  the  next  test;  one  received  6  visits,  the  other,  13  during  a  unit 
period.  The  calyx-lobes  and  corolla  were  cut  from  the  more  attractive 
flower,  which  then  received  no  visits  in  contrast  to  12  for  the  other. 

Lovell  explains  the  visits  to  the  mutilated  flowers  of  Digitalis  purpurea 
in  Plateau's  experiments  as  due  primarily  to  memory  of  place,  though 
the  corolla  stump  itself  was  not  entirely  inconspicuous,  and  cites  in  illus- 
tration the  visits  of  bees  for  a  month  and  a  half  afterward  to  a  window 
where  they  had  obtained  honey.  Bees  were  trained  to  visit  a  red-glass 
slide  with  honey,  and  this  was  put  in  various  positions,  and  a  plain  slide 
added.  All  of  these  were  found  in  6  to  20  minutes  as  a  consequence  of 
the  reflected  light,  the  color,  and  the  odor,  and  this  is  regarded  as 
explaining  why  bees  readily  passed  under  the  green  leaves  used  by  Pla- 
teau for  masking  dahlia  heads.  These  experiments  were  not  well  adapted 
to  the  purpose  and  afford  an  insufficient  basis  for  the  conclusion  that 
bright  colors  are  not  advantageous  to  flowers. 

Can  bees  distinguish  colors? — In  order  to  test  the  statement  of  Pla- 
teau that  flowers  might  as  well  be  green  as  bright-colored  and  that  of  Bethe 
that  bees  have  no  ability  to  acquire  experiences  or  to  modify  them,  Lovell 
has  repeated  and  extended  the  experiments  of  Lubbock  with  colored  strips 
of  paper  (1910:673).  After  a  bee  had  been  accustomed  to  visit  a  blue 
strip  with  honey,  strips  of  other  color  were  added  or  exchanged  with  it 
in  various  ways.  Given  a  choice  between  blue  and  red,  the  bee  went  4 
times  to  the  former  and  once  to  the  latter.  When  blue,  red,  and  yellow 
were  employed,  blue  alone  was  visited.  With  a  wider  range  of  choice  the  bee 
went  to  blue  8  times,  black  twice,  and  once  to  red,  yellow,  and  white, 
the  choice  of  some  other  color  than  blue  occurring  only  after  the  slides 
had  been  exchanged  or  the  color  changed.  Out  of  the  total  of  21  visits, 
15  were  made  to  blue  and  not  more  than  2  to  any  other  color,  the  bee  en- 
deavoring to  be  constant  to  blue  in  spite  of  loss  of  time  and  effort.  When 
a  yellow  and  a  plain  slide  were  used,  the  bees  made  20  visits  to  the  first 
in  30  minutes,  entirely  ignoring  the  second;  flies  went  alone  to  the  yellow, 
and  the  wasps  went  to  it  in  all  but  two  cases.  These  results  indicate  that 
Plateau  was  in  error  in  assuming  that  artificial  colors  appear  different 
from  natural  ones  to  the  bee. 


RECENT   INVESTIGATIONS.  195 

Lovell  has  also  repeated  the  experiments  of  Mueller  with  colored  co- 
rollas, making  use  of  the  yellow  rays  of  sunflower,  the  blue  perianth  of 
larkspur,  and  the  red  corolla  of  balsam.  A  bee  accustomed  to  the  sun- 
flower yellow  made  9  visits  to  it  and  one  to  blue,  and  in  other  experiments 
with  these  slides  the  bees  discriminated  readily  between  the  colors.  When 
bees  trained  to  red  were  given  a  choice  between  a  red  slide  and  a  plain 
one,  they  made  46  visits  to  the  one  and  but  8  to  the  other.  To  determine 
the  effect  of  habit  in  this  case,  a  blue  slide  was  substituted  for  the  plain  one; 
the  first  visits  were  8  to  red  and  2  to  blue,  but  at  the  end  this  had  changed 
to  3  for  red  and  7  for  blue,  the  respective  totals  being  22  and  24.  A  number 
of  instances  are  cited  from  the  experience  of  practical  apiarists  to  show 
that  bees  distinguish  colors  readily,  and  it  is  stated  that  "it  may  well  be 
doubted  whether  they  would  ever  have  been  capable  of  making  long  journeys 
afield  for  nectar  and  pollen,  if  this  visual  power  had  been  wanting." 

When  a  bee  trained  to  blue  was  given  a  choice  between  seven  or  eight 
colors,  it  remained  constant  to  blue  or  purple  for  several  visits,  but  its 
fidelity  to  them  was  weakened  by  repeated  transpositions,  until  similar- 
ity of  form,  honey,  and  odor  prevailed  over  the  difference  in  color  and 
visits  were  then  made  indiscriminately.  In  nature  a  bee  usually  finds 
in  one  flower  only  a  part  of  a  load  of  nectar  and  is  compelled  to  go  to  other 
blossoms;  if  these  are  alike  in  form  they  will  then  be  visited  regardless 
of  differences  in  color,  especially  when  a  number  of  bees  are  present.  In 
conclusion,  Lovell  states  that  bees  easily  distinguish  colors  whether  arti- 
ficial or  natural  and  are  more  strongly  attracted  by  a  colored  than  a  plain 
slide.  Bees  trained  to  a  certain  color  tend  to  return  to  it  habitually,  but  they 
quickly  learn  to  ignore  the  color  differences  when  it  is  to  their  advantage. 

The  pollination  of  green  flowers. — Lovell  (1912:83)  discusses  the  re- 
lation of  insects  to  green  flowers  and  points  out  that  the  phylogeny  of 
such  flowers  as  developed  by  Bessey  (1897,  1907)  strongly  supports  the 
view  that  they  are  not  well  adapted  to  pollination  by  insects.  He  ad- 
mits that  bees  will  collect  sweet  liquids  from  green  or  dull-colored  sur- 
faces, after  they  have  once  been  found,  but  states  that  this  does  not  prove 
that  bright  colors  are  not  an  advantage  to  flowers.  When  a  bouquet  of 
Gerardia  purpurea  was  placed  in  front  of  a  hive,  it  received  little  attention, 
but  when  two  clusters,  one  normal  and  the  other  decorollate,  were  provided 
with  honey,  the  former  received  many  visits  and  the  latter  none,  until 
later,  when  the  bees  discovered  the  honey  on  them.  In  order  to  vary  the 
conditions  under  which  the  objects  were  exposed,  bees  were  trained  to 
visit  a  small  dull-gray  board  bearing  a  small  quantity  of  honey,  raised 
on  a  support  2  feet  high.  A  slide  prepared  from  the  blue  perianth  of  a 
larkspur  and  provided  with  honey  was  placed  on  the  grass  3  feet  from  the 
support  and  honey  was  also  placed  on  a  dandelion  leaf  5  feet  away  and  3 
feet  from  the  support.  As  soon  as  the  honey  on  the  feeder  was  exhausted, 
the  bees  began  to  circle  in  the  air.  In  a  few  minutes  1  bee  had  found  the 
blue  slide  and  in  25  minutes  5  bees  found  it,  though  none  had  discovered 
the  honey  on  the  leaf.  Two  days  later  the  experiment  was  repeated,  3 
bees  finding  the  blue  slide  within  2  minutes  after  the  honey  had  disappeared 
from  the  feeder.  In  7  minutes  there  were  8  bees  on  the  slide  and  none  on 
the  green  leaf,  1  bee  finding  the  latter  5  minutes  later.   Two  poles  4.5  feet 


196  PRINCIPLES  AND   CONCLUSIONS. 

high  were  then  placed  6  feet  from  the  support  and  6  feet  apart;  the  top 
of  one  was  covered  with  a  large  amount  of  honey,  while  to  the  top  of  the  other 
was  attached  a  cluster  of  yellow  immortelles  many  years  old.  Within  3 
minutes  after  the  honey  disappeared  from  the  feeder  there  were  3  bees 
and  a  fly  on  the  flowers,  but  none  on  the  free  honey;  later  there  were  6 
bees  and  1  fly  on  the  flowers  and  1  bee  on  the  free  honey,  the  total  num- 
ber of  visitors  to  the  flowers  being  three  times  greater  than  to  the  free 
honey.  When  the  poles  were  transposed  and  a  single  immortelle  placed 
on  the  one  that  had  the  supply  of  honey  previously,  both  being  provided 
with  honey,  the  cluster  showed  10  insects  at  the  same  time  that  the  single 
flower  gave  4. 

In  later  experiments  a  yellow  immortelle  with  honey  was  placed  9  feet 
from  the  feeder  and  a  considerably  larger  apple-leaf  with  honey  at  a  equal 
distance  on  the  opposite  side.  Three  bees  came  to  the  flower  and  none 
to  the  leaf,  the  small  number  apparently  due  to  the  fact  that  they  were 
looking  for  sugar  sirup  which  they  had  been  eating  on  the  feeder.  The 
number  of  visitors  was  larger  in  other  cases,  but  in  spite  of  this  the  leaf 
did  not  receive  a  single  visit.  When  a  head  of  golden  glow  and  the  end 
of  a  spike  of  Amarantus  were  used,  the  head  yielded  18  visits  to  8  for  the 
spike,  but  when  they  were  laid  side  by  side,  there  were  15  visits  to  the  golden 
glow  to  3  to  the  spike  in  one  case,  and  18  to  5  in  another.  In  further  studies 
with  a  green  and  bright-colored  object  placed  on  a  green  background 
or  with  conspicuous  and  inconspicuous  objects,  which  extended  over  three 
seasons,  there  were  no  visits  to  the  inconspicuous  objects  in  6  cases,  while 
in  the  others  the  number  of  visits  to  the  conspicuous  object  was  usually 
two  or  three  times  greater.  The  preference  was  sufficiently  marked  to 
account  for  the  development  of  color  contrast  in  flowers  and  shows  that 
the  experiments  and  observations  of  Plateau  on  green  or  greenish  flowers 
were  fallacious. 

Conspicuous  flowers  rarely  visited  by  insects. — In  testing  Plateau's 
conclusion  that  bright  color  is  without  significance  because  certain  con- 
spicuous flowers  are  commonly  neglected,  Lovell  (1914:147)  made  ob- 
servations and  experiments  on  some  of  the  same  species,  in  addition  to 
others.  The  nectarless  flowers  of  Clematis  jackmanni  were  not  only  found 
to  be  visited,  but  the  number  of  visitors  was  greatly  increased  by  putting 
sugar  sirup  on  some  of  them,  showing  that  the  presence  of  an  agreeable 
odor  was  unnecessary,  contrary  to  Plateau's  assumption.  It  was  deter- 
mined that  the  real  reason  for  the  general  absence  of  visits  to  the  garden 
pea  and  the  sweet  pea  is  the  inability  of  most  pollinators  to  depress  the  keel 
and  open  the  flower.  In  these  flowers  neither  color  nor  odor  will  induce 
frequent  visits,  since  nothing  is  to  be  gained  by  them,  but  the  addition 
of  an  odorless  sirup  causes  bees  to  go  to  them  in  large  number.  Similar 
results  were  obtained  in  the  case  of  petunia,  the  addition  of  sugar  sirup 
bringing  many  bees  and  small  Diptera,  and  the  honey-bees  continuing 
to  come  for  many  days  after  the  sirup  was  gone.  In  the  case  of  a  variety 
of  Pelargonium  zonale  with  neither  nectar  nor  pollen,  no  insect  visits  were 
observed  to  the  normal  flowers,  but  the  application  of  sugar  sirup  ultimately 
brought  them,  the  bees  repeatedly  searching  the  normal  umbels  after  the 
supply  was  exhausted.    Later  they  flew  to  a  bed  of  Portvlaca  grandiflora, 


RECENT   INVESTIGATIONS.  197 

which  is  habitually  ignored,  and  inspected  flower  after  flower,  but  rarely 
alighting.  The  use  of  sugar  sirup  also  brought  visitors  to  other  flowers 
ordinarily  neglected,  such  as  zinnia  and  the  scarlet  runner. 

Interesting  instances  are  given  of  the  role  played  by  variations  in  the 
length  of  the  corolla  of  red  clover  and  the  amount  of  nectar  in  alfalfa 
in  determining  the  visits  of  honey-bees,  and  many  cases  are  cited  to  show 
that  the  latter  occasionally  make  careful  examination  of  flowers  commonly 
neglected.  Such  visits  are  infrequent  because  the  bees  remember  their 
inability  to  obtain  food.  In  the  aggregate  they  waste  much  time  in  fruit- 
less visits  to  flowers  that  yield  no  booty  for  one  reason  or  another,  but 
this  waste  is  reduced  to  a  minimum  by  their  ability  to  learn  from  expe- 
rience. Thus,  insects  do  perceive  the  colors  and  forms  of  neglected  flowers, 
and  the  rarity  of  their  visits  is  the  result  of  recalling  the  absence  of  nectar 
or  pollen  and  not  because  the  flowers  lack  an  agreeable  odor,  which, 
moreover,  is  often  not  the  case. 

Response  of  honey-bees  to  colored  artefacts. — Turner  (1910:257) 
has  carried  out  investigations — 

"To  see  if,  in  the  field,  bees  can  be  trained  to  respond  to  colored  artefacts,  and, 
after  a  bee  has  thoroughly  learned  to  collect  honey  from  an  artefact  of  a  certain  color, 
to  see  if  it  can  select  those  of  that  color  from  numerous  others  of  a  different  color; 
first,  when  the  artefacts  to  be  selected  contain  honey  and  the  others  do  not;  second, 
when  some  of  each  kind  contain  honey;  third,  when  none  of  the  artefacts  contain 
honey;  fourth,  when  the  brightness  content  of  the  artefact  to  be  selected  is  changed 
without  altering  the  hue.  In  furthering  the  first  aim,  honey  was  placed  on  disks  of 
a  certain  color  and  exposed  in  a  field  from  which  a  large  number  of  bees  were  col- 
lecting honey.  At  first  these  disks  were  not  attended  to;  but  after  a  lapse  of  several 
hours  a  few  bees  began  to  collect  from  them.  After  a  few  bees  had  acquired  the  habit 
of  collecting  from  disks  of  a  certain  color,  three  different  series  of  experiments  were 
conducted;  one  with  disks,  one  with  cornucopias,  and  one  with  small  boxes,  each 
provided  with  a  small  opening.  In  each  of  these  series  a  large  number  of  artefacts  of 
two  colors,  half  of  which  were  of  the  color  of  the  disks  from  which  the  bees  had  learned 
to  collect  honey,  were  scattered  promiscuously  among  the  flowers  from  which  the 
bees  were  foraging.  The  artefacts  of  the  color  from  which  the  bees  had  learned  to 
collect  honey  were  supplied  with  honey,  the  others  were  not.  All  of  the  artefacts 
containing  honey  were  visited  by  numerous  bees;  no  bees  visited  the  others.  Control 
artefacts  of  the  color  from  which  the  bees  were  collecting  honey  were  well  supplied 
with  the  latter  and  placed  in  portions  of  the  field  where  the  bees  had  not  been  trained 
to  feed  from  artefacts.  Although  the  bees  were  numerous,  these  artefacts  were  not 
visited.  At  intervals  artefacts  of  the  color  from  which  the  bees  had  not  been  trained 
to  forage  were  supplied  with  honey  and  scattered  among  the  others.  As  a  rule  these 
were  not  visited.  At  the  close  of  both  the  second  and  third  series  of  experiments, 
all  of  the  artefacts  were  removed  from  the  field;  and  two  artefacts,  one  of  each  color, 
both  new  and  neither  containing  honey,  were  exposed  in  the  field.  In  a  few  minutes, 
the  artefact  of  the  color  that  had  formerly  marked  those  that  contained  honey  was 
completely  packed  with  struggling  bees.  No  bees  entered  the  other  artefact.  In 
each  series  the  artefacts  were  distributed  in  both  the  sunshine  and  the  shadow.  All 
were  equally  visited  by  bees.  Since  the  brightness  content  in  the  two  cases  was 
different  while  the  color  was  the  same,  it  was  concluded  that  the  bees  were  reacting 
to  color  as  such.  It  is  thought  that  these  experiments  prove  that  bees  can  discriminate 
between  colors." 


198  PRINCIPLES  AND   CONCLUSIONS. 

Pattern  vision  in  the  honey-bee. — In  experiments  on  this  subject, 
Turner  (1911:249)— 

"Made  use  of  pasteboard  boxes  like  those  employed  in  his  experiments  on  color 
vision  in  the  same  insect.  He  constructed  artefacts  showing  seven  different  color 
patterns.  Bees  which  had  been  trained  to  gather  honey  from  one  pattern  were  tested 
to  see  if  they  could  choose  this  pattern  from  one  or  more  of  the  others.  In  some  cases 
the  artefact  of  the  pattern  to  be  chosen  contained  honey,  while  the  rest  had  none; 
in  other  cases  there  was  honey  on  some  of  the  artefacts  of  all  patterns,  and  in  still 
others  there  was  no  honey  on  any  of  the  artefacts.  Five  hundred  and  eight  correct 
selections  out  of  518  were  made,  indicating  that  color  patterns  are  perceived  by  bees. 
Since  they  can  distinguish  both  color  and  pattern,  no  evidence  can  be  drawn  from  the 
visual  powers  of  bees  against  the  hypothesis  that  colors  and  patterns  in  flowers  are 
adapted  to  secure  the  visits  of  insects." 

Experiments  with  cotton  blossoms. — Allard  (1911:607)  has  made 
a  large  number  of  interesting  experiments  with  single  cotton  blossoms. 
The  normal  flower,  modified  flower,  and  control  were  disposed  at  the  corners 
of  a  triangle  and  about  4  feet  apart,  or  in  a  line  in  the  same  row.  Petals 
pinned  to  a  stem  received  as  many  inspections  as  the  normal  flower,  almost 
all  of  them  being  made  by  Melissodes.  The  number  of  entrances  was  less 
than  one-fifteenth  the  number  of  inspections,  and  at  all  times  the  actual 
visits  were  few.  When  the  petals  of  one  of  the  same  group  of  flowers  were 
removed,  the  inspections  dropped  from  81  to  4,  though  they  actually  in- 
creased for  the  other  normal  flower.  Replacing  the  petals  brought  the 
inspections  up  to  those  for  the  normal,  but  when  cloth  petals  from  an  artificial 
rose  were  employed,  the  number  dropped  to  4  in  comparison  with  48  for  the 
normal  control  and  65  for  the  petals  alone.  Five  cotton  petals  were  then 
placed  over  the  cloth  ones  and  the  number  of  inspections  again  rose  to 
a  point  slightly  above  that  for  the  control.  The  next  installation  con- 
sisted of  a  normal  blossom  in  situ,  one  pinned  in  position,  and  an 
artificial  half-opened  bud  made  by  pinning  normal  petals  together  and 
wrapping  a  piece  of  green  cotton  leaf  about  the  base.  The  latter  received 
practically  the  same  number  of  inspections  as  the  most  visible  control.  This 
was  next  modified  by  concealing  one  of  the  normal  flowers  so  that  it  was 
visible  only  from  above;  this  yielded  1  inspection  to  12  for  the  control 
and  40  for  the  artificial  bud.  Removing  the  disguise  caused  the  flower 
to  be  inspected  twice  as  often  as  the  control.  The  substitution  of  crepe- 
paper  petals  led  to  the  reduction  of  inspections  to  2  in  contrast  to  16  for 
the  control,  while  placing  three  real  petals  on  the  paper  ones  increased 
them  to  11  in  comparison  to  7  for  the  control  and  21  for  the  artificial  bud. 

The  following  installation  comprised  a  single  real  petal  pinned  to  a 
stem,  an  artificial  bud  made  by  wrapping  a  portion  of  a  cotton  leaf  about 
the  base  of  5  petals  rolled  together  and  a  normal  in  situ;  these  received 
2,  8,  and  3  inspections  respectively.  A  single  petal  in  competition  with 
a  normal  blossom  alone  obtained  16  inspections  to  26  for  the  latter.  In 
the  following  experiments  the  flowers  were  on  3  consecutive  plants  in  the 
same  row.  The  first  consisted  of  a  flower  of  bindweed  between  two  normal 
flowers  pinned  in  position,  which  attracted  attention  as  often  as  the  nor- 
mals, but  was  entered  less  frequently.  When  the  petals  were  removed 
from  one  of  the  controls,  this  received  no  inspections  to  19  for  the  bindweed 


RECENT   INVESTIGATIONS.  199 

and  20  for  the  normal  control.  When  a  single  petal  was  placed  on  the  de- 
corollate  flower,  the  latter  yielded  8  inspections  to  9  for  a  single  petal 
pinned  to  the  stem  and  27  for  a  normal  flower;  changing  the  relative 
position  of  the  three  gave  27,  8,  and  22  inspections.  Placing  the  smaller 
brighter  yellow  blossom  of  an  Asiatic  cotton  between  two  normal  flowers 
of  the  American  variety  resulted  in  14  inspections  for  the  former  and  20 
and  29  for  the  latter  in  one  case,  and  10,  16,  and  20  in  another,  while  putting 
the  foreign  flower  at  one  end  of  the  series  gave  3,  10,  and  11  respectively 
in  one  instance  and  11,  12,  9  in  the  other.  A  day-old  blossom  of  a  deep 
reddish-purple  color  received  12  visits  to  26  for  a  recently  opened  cream- 
colored  one.  Four  experiments  with  two  controls  and  a  normal  blossom 
with  honey  added  at  the  base  of  the  petals,  arranged  in  varying  order, 
gave  respectively  62,  64,  and  66  inspections,  the  actual  visits  being  but  2 
for  the  flower  with  honey  to  27  for  the  other  two. 

The  petals  of  a  normal  bloom  were  covered  on  both  sides  with  cotton 
leaves  cut  to  match  and  a  drop  or  two  of  honey  added.  When  this  was 
exposed  with  a  control  with  honey  and  one  without,  the  inspections  were 
respectively  0,  34,  and  25,  the  actual  entrances  being  0,  2,  and  6.  In  the 
next  installation  the  pieces  of  leaf  were  removed  from  the  outside  of  the 
corolla  and  this  was  exposed  with  a  normal  flower  and  one  with  the  petals 
removed.  The  respective  inspections  were  9,  11,  and  1,  while  the  actual 
visits  were  negligible.  When  one  bud  due  to  open  the  next  day  was  pulled 
fully  open  and  another  but  partly  so,  the  first  was  inspected  15  times  to 
twice  for  the  latter  and  24  for  the  normal,  the  latter  receiving  14  visits 
to  none  for  the  other  two.  To  entirely  eliminate  the  effect  of  odor,  a  glass 
plate  was  fixed  before  a  flower  and  leaves  drawn  in  about  the  edges  to  con- 
ceal most  of  the  plate  but  leave  the  flower  fully  visible.  This  received  18 
inspections  in  contrast  to  37  for  the  normal.  When  a  flower  was  placed 
in  a  box  with  a  glass  face,  it  was  inspected  twice  to  5  times  for  the  control. 
With  a  crepe-paper  blossom  of  the  proper  color  added,  the  boxed  flower 
was  inspected  once,  the  normal  8  times,  and  the  imitation  3  times.  In  the 
final  experiments,  detached  petals  were  usualty  inspected,  but  the  numbers 
were  too  small  to  be  very  significant. 

The  simplicity  and  variety  of  Allard's  experiments,  coupled  with  the 
use  of  single  flowers  and  constant  controls,  give  his  results  an  excep- 
tional value.  They  emphasize  the  attractive  value  of  the  color  at  the  ex- 
pense of  odor  and  suggest  that  the  latter  merely  guides  bees  from  a  distance 
or  from  one  field  to  another.  The  discrimination  between  artificial  flowers 
and  normal  ones  is  thought  to  depend  upon  perceptible  differences  in  color 
and  texture  rather  than  to  the  presence  of  repellent  odors  from  the  material 
and  support  the  view  that  bees  develop  keen  powers  of  discernment  as 
to  the  structural  details  of  flowers. 

Color  sense  and  memory  in  the  honey-bee. — Dobkiewicz  (1912:664) 
carried  out  three  series  of  experiments  dealing  respectively  with  the  color- 
•  sense,  memory,  and  learning  ability  of  the  honey-bee.  The  first  series 
employed  crude  artificial  flowers  of  yellow  or  red  paper  placed  at  the  same 
spot  in  a  clover  field.  No  visits  were  made  to  installations  of  10  yellow  or 
10  red  artefacts  without  honey,  or  at  first  to  5  of  each  color  with  and  with- 
out honey.     For  the  next  experiment  the  blue  artefacts  were  removed, 


200  PRINCIPLES  AND   CONCLUSIONS. 

after  which  a  single  bee  appeared,  soon  followed  by  two  others.  A  half  hour 
later  the  honey  flowers  were  actively  sought,  while  those  without  honey 
were  completely  neglected.  When  the  yellow  flowers  were  more  widely 
separated  and  the  blue  ones  so  interspersed  that  one  with  honey  occupied 
the  former  position  of  a  similar  yellow  one,  the  blue  imitations  were  neither 
inspected  nor  visited,  though  the  yellow  were  busily  probed.  Placing  the 
two  kinds  of  yellow  artefacts  in  pairs  caused  those  without  honey  to  be 
often  inspected,  but  the  bees  quickly  learned  the  position  of  the  honey  ones 
and  paid  no  further  attention  to  the  others.  Further  experiments  likewise 
showed  that  when  the  bees  did  not  at  first  know  all  the  honey  artefacts, 
it  was  necessary  for  them  to  make  orienting  flights  over  the  two  kinds. 
However,  the  flights  of  inspection  over  the  flowers  without  honey  gradually 
diminished  to  the  point  of  disappearance.  With  respect  to  memory,  the 
second  series  of  experiments  indicated  that  colored  objects  do  not  attract 
bees  that  are  busily  at  work  if  they  have  had  no  previous  experience  with 
imitations.  However,  when  they  have  repeatedly  found  honey  in  an  arte- 
fact of  a  certain  color  in  one  spot,  the  color  continues  to  exert  attraction 
even  when  honey  is  absent,  and  small  displacements  of  position  are  imma- 
terial. It  was  also  demonstrated  that  bees  habituated  to  gather  from  honey 
artefacts  at  a  certain  time,  namely,  11  to  1  o'clock,  did  not  react  to  them 
at  a  different  time,  showing  that  they  take  note  of  time  as  well  as  of  color 
and  place.  Further  experiments  showed  that  the  bees  were  able  to  make 
use  of  two  colors  in  adjusting  themselves  to  new  conditions  and  that  they 
utilize  their  sense  of  color  in  different  and  unexpected  relations.  In  short, 
they  are  not  reflex  machines,  but  their  behavior  has  the  stamp  of  purposeful, 
intentional  acts. 

Frisch's  researches. — Sense  of  color  and  form  in  the  honey-bee. — 

Frisch  has  discussed  the  color  and  form  sense  of  the  honey-bee  in  a  mono- 
graph of  fundamental  importance  (1914),  as  well  as  in  shorter  articles 
(1913,  1919).  At  the  present  time  it  is  possible  only  to  indicate  the  scope 
of  his  treatment  and  the  general  method,  and  to  give  his  conclusions.  The 
original  itself  must  be  studied  by  all  those  who  wish  to  carry  on  accurate 
work  under  controlled  conditions.  The  treatise  is  divided  into  the  follow- 
ing main  sections:  (1)  demonstration  of  a  color  sense;  (2)  nature  of  the 
color  sense;  (3)  the  color  sense  of  the  honey-bee  and  flower  colors;  (4)  sense 
of  form  and  its  significance  in  flower  visits ;  (5)  unsuccessful  training  experi- 
ments with  unnatural  forms;  (6)  biological  notes;  (7)  practical  significance 
of  painting  hives  in  color.  The  method  of  experiment  consisted  essentially 
in  training  bees  to  come  to  a  watch-glass  of  honey  placed  on  a  particular 
color  and  following  their  behavior  when  such  colored  squares  were  variously 
arranged  among  gray  ones,  ranging  through  all  possible  shades  from  white 
to  black  and  likewise  provided  with  glasses  of  honey.  After  two  days 
training  with  two  papers  of  dull  yellow  disposed  among  30  gray  ones,  two 
new  yellow  papers  and  watch-glasses,  unused  and  hence  free  from  the  odor 
of  bees,  were  placed  in  a  different  position  from  the  first  two,  which  were 
removed  and  gray  ones  substituted.  All  the  watch-glasses  were  then  filled 
with  sugar  solution,  thus  making  the  conditions  on  all  the  papers  identical, 
except  for  color  and  brightness.  Thus,  if  the  bees  were  entirely  color 
blind  they  would  see  yellow  only  as  a  certain  degree  of  brightness  without 


RECENT   INVESTIGATIONS.  201 

color  and  would  visit  the  corresponding  shade  of  gray  in  similar  number. 
If  they  saw  color  as  such,  the  yellow  papers  should  receive  more  visits  than 
all  the  gray  ones.  This  is  what  actually  happened.  The  bees  flew  without 
hesitation  to  the  yellow  papers  and  crowded  together  on  these  about  the 
sugar-solution,  while  the  watch-glasses  of  this  solution  on  the  gray  papers 
remained  neglected.     Frisch's  conclusions  were  as  follows: 

1.  Bees  possess  a  sense  of  color.  This  is  proved  by  the  fact  that  if  they  were  totally 
color-blind  they  would  see  each  color,  for  example,  blue,  only  as  gray  of  a  certain  brightness. 
In  a  series  of  gray  papers  that  grade  insensibly  from  white  to  black  must  occur  a  gray  paper 
that  would  be  identical  to  the  bee  with  a  blue  one  in  form,  extent,  and  surface  character. 
Once  trained,  however,  it  is  able  to  distinguish  the  blue  paper  with  certainty  from  all  the 
shades  of  gray.  The  gradations  of  the  gray  series  were  sufficiently  fine,  as  demonstrated 
by  the  fact  that  training  for  a  particular  shade  of  the  series  was  unsuccessful.  The  objection 
that  the  bees  may  have  recognized  the  colored  paper  by  means  of  a  particular  odor  imper- 
ceptible to  us  is  removed  by  the  fact  that  the  experiments  gave  the  same  results  when 
the  colored  and  gray  papers  were  covered  with  a  glass  plate  or  sealed  in  a  glass  tube. 

2.  The  bee  confuses  red  with  black  and  blue-green  with  gray.  It  distinguishes  only 
"warm"  and  "cold"  colors  and  mixes  orange-red  with  yellow  and  with  green,  blue  with 
violet  and  purple-red.  Thus,  its  color  sense  shows  a  close  agreement  with  that  of  a 
man  color-blind  to  red  and  green  (protanopic). 

3.  The  colors  that  are  not  seen  as  such  by  the  bee,  such  as  blue-green  and  pure  red,  are 
extraordinarily  rare  in  the  flowers  of  our  flora.  This  supports  the  view  that  the  colors  of 
flowers  have  developed  in  adaptation  to  their  pollinators,  and  all  the  more  since,  in  exotic 
flowers  adapted  to  pollination  by  birds,  scarlet-red  blossoms  predominate  and  blue  ones 
are  strikingly  infrequent.  In  many  flowers  are  found  several  colors  combined  which 
contrast  strongly.  Such  "contrast  colors"  have  been  regarded  as  adaptations  to  insect 
visits,  especially  when  they  appear  in  the  form  of  nectar  guides.  However,  our  new 
knowledge  indicates  that  color  differences  which  are  conspicuous  to  our  eyes  can  not  be 
assumed  to  be  such  for  the  eyes  of  the  insects,  but  closer  examination  shows  that  this 
presents  no  serious  difficulty.  We  find  that  the  varicolored  flowers  combine  almost  exclu- 
sively such  colors  as  stand  out  distinctly  from  each  other  in  the  bee's  eye.  On  the  other 
hand,  the  biological  significance  ascribed  to  changes  of  color  during  anthesis  is  not  to  be 
accepted  in  the  fullest  sense. 

It  has  appeared  a  striking  fact  to  students  of  flower  biology  that  blossoms  with  the  most 
complete  adaptation  to  allogamy  and  particularly  fitted  to  the  visits  of  honey-bees  and 
bumble-bees  should  be  blue  or  red-purple.  This  has  been  explained  by  the  assumption 
that  such  colors  are  the  favorite  ones  of  bees.  On  the  contrary,  my  experiments  show 
that  for  the  bee's  eyes  blue  and  red-purple  contrast  most  strongly  with  the  green  of  leaves, 
and  hence  range  themselves  readily  with  the  other  characters  by  which  the  bee  flowers 
reveal  their  greater  adaptation  to  insect  pollination  in  contrast  with  the  more  primitive 
flowers  of  this  kind. 

4.  From  the  observations  on  constancy  it  follows  that  bees  recognize  the  flowers  of 
one  species  as  belonging  together  and  hence  distinguish  them  certainly  from  those  of 
another  species.  Since  they  possess  no  finer  sense  of  discrimination  for  color  nuances, 
they  must  consequently  utilize  other  features  than  flower  color.  Thus  it  may  be  shown 
that  form  and  combinations  of  color  serve  bees  as  indicators,  and  the  significance  of  nectar 
guides  is  partly  to  be  sought  in  this  connection. 

5.  It  is  of  psychological  interest  that  the  training  of  bees  is  unsuccessful  when  it  demands 
of  them  the  discrimination  of  forms  that  are  completely  unknown  to  them  in  nature,  e.  g., 
geometric  figures. 

6.  The  question  whether  color  striping  of  the  hive  facilitates  the  return  of  the  bees 
to  the  proper  hive  must  be  answered  in  the  affirmative.  How  closely  the  bees  observe 
hive-color  and  use  it  as  a  guide  is  shown  by  the  fact  that  returning  bees  can  all  be  decoyed 
into  a  wrong  empty  hive  by  a  change  of  color.  Misled  by  the  color  of  the  hive,  they  even 
seek  to  enter  occupied  hives,  where  they  are  received  in  the  most  unfriendly  manner. 

The  supposed  color  sense  of  the  honey-bee. — In  a  series  of  papers 
(1913-1919),  Hess  has  imitated  Plateau  in  challenging  all  the  studies  and 


202  PRINCIPLES  AND   CONCLUSIONS. 

conclusions  as  to  the  ability  of  bees  to  distinguish  colors  as  such.  It  is 
now  impossible  to  deal  with  his  experiments  and  criticisms  in  detail,  and 
it  must  suffice  to  give  the  summaries  of  the  two  papers  that  treat  this 
question  directly.  These  will  serve  also  to  reveal  the  attitude  of  the  author, 
who  goes  far  beyond  Plateau  in  rejecting  unqualifiedly  the  results  of  those 
who  do  not  agree  with  him. 

"It  has  been  demonstrated  that  the  earlier  conclusions  of  Lubbock  and  Forel,  as  well 
as  the  later  ones  of  Frisch,  in  accordance  with  which  it  is  possible  to  train  bees  to  discrimi- 
nate a  particular  color,  are  incorrect.  If  the  colors  are  presented  under  conditions  other- 
wise identical,  the  bees  find  it  wholly  impossible  to  habituate  themselves  to  a  certain  color 
and  to  respond  to  it.  The  errors  of  the  earlier  investigators  are  in  part  to  be  ascribed  to 
the  fact  that  they  either  ignored  the  contributing  factors  emphasized  by  me  or  failed  to 
take  them  sufficiently  into  account. 

"  Up  to  the  present  time  not  a  single  fact  has  been  adduced  that  makes  even  probable  the 
assumption  that  bees  possess  a  color  sense  comparable  with  ours.  On  the  contrary,  my 
earlier  researches  with  spectral  and  other  rays  as  well  as  the  later  ones  with  colored  papers 
refute  this  opinion  conclusively.  In  virtue  of  the  results  contributed  by  me,  which  are 
readily  demonstrable,  the  view  of  Sprengel  as  to  the  significance  of  flower  color  in  insect 
attraction  can  no  longer  be  maintained."     (1913: 105.) 

"It  has  been  demonstrated  that  every  training  experiment  with  bees,  which  has  been 
thought  to  prove  their  color  sense,  affords  complete  support  to  my  researches  which  show 
their  total  color-blindness.  Moreover,  Frisch's  record  shows,  in  entire  agreement  with 
mine,  that  bees  supposedly  trained  to  blue  or  yellow  were  unable  to  distinguish  the  two 
colors,  but  much  more  frequently  confused  one  with  the  other  or  with  gray. 

"The  inadequacy  of  the  method  of  training  experiments  is  forcibly  exhibited  by  these 
new  observations  and  measurements.  Furthermore,  the  objections  recently  raised  from 
the  zoological  side  to  my  investigations  are  vitiated  by  the  results  given  here.  Finally, 
even  Frisch  himself  has  removed  the  last  prop  from  the  concept  of  color  sense  in  the  bees 
by  his  training  experiments  and  the  Freiburg  results."     (1918:365.) 

Frisch  (1919:122)  has  made  an  effective  rejoinder  to  Hess's  statements, 
as  is  indicated  by  the  following  excerpts : 

"Hess  begins  his  real  objections  with  the  surprising  assertion  that  my  record  shows 
that  the  bees  were  unable  to  distinguish  blue  and  yellow  from  gray,  and  also  blue  from 
yellow.  I  wish  to  ask  him  how  he  can  advance  such  a  statement  when  he  must  have  seen 
from  my  record  that  the  bees  trained  to  yellow  discerned  the  latter  and  discriminated 
between  it  and  all  the  shades  of  gray  in  all  seven  experiments  in  which  a  yellow  paper  was 
exposed  in  the  gray  series;  that  further,  the  bees  trained  to  blue  selected  this  color  and 
distinguished  it  from  the  gray  shades  in  the  entire  15  experiments  with  blue  similarly  exposed; 
that  bees  trained  to  yellow  sought  this  in  overwhelming  majority  in  competition  with  blue 
and  purple  in  all  eight  experiments,  and  finally  that  bees  trained  to  blue  chose  blue  and 
purple  just  as  decisively  in  25  of  the  26  tests  with  the  complete  color  series,  the  exception 
being  readily  explained  by  the  circumstances  (p.  126). 

"I  have  shown  that  bees  trained  to  blue  for  two  days  were  able  to  distinguish  with 
certainty  a  blue  paper,  which,  according  to  Hess,  they  see  as  a  colorless  gray  of  a  particular 
shade,  from  gray  papers  of  any  shade.  In  order  to  remove  the  objection  that  they  directed 
themselves  to  the  blue  paper  by  virtue  of  an  odor  imperceptible  to  us,  all  the  papers  were 
covered  by  a  glass  plate.  When  the  mass  of  bees  above  the  blue  paper  were  brought  upon 
a  gray  one  by  moving  the  glass  plate,  the  mass  dissolved  within  ^  to  J^  minute  and  a  new 
one  formed  upon  the  blue"  (p.  135). 

Seasonal  change  in  the  response  to  honey. — Zander  (1913:711) 
found  that,  while  honey  exposed  in  summer  stood  day  after  day  without 
visits  from  honey-bees,  in  agreement  with  the  results  of  Forel,  it  was  sought 
by  hosts  of  them  in  September.  This  led  him  to  make  similar  tests  at  inter- 
vals of  about  two  weeks  from  the  end  of  April  to  the  beginning  of  October. 


RECENT   INVESTIGATIONS.  203 

The  honey  was  placed  in  a  small  porcelain  dish  covered  with  gauze,  so  that 
the  odor  could  escape  but  the  honey  itself  could  not  be  reached  and  thus 
exhausted.  This  was  exposed  on  the  threshold  or  the  top  of  a  hive  and 
observed  for  a  quarter  to  a  half  hour  during  the  period  of  the  best  morning 
flight,  the  temperature,  humidity,  wind  direction,  and  condition  of  the  sky 
being  recorded,  as  well  as  the  honey  increase  of  a  test  hive  and  the  kind  and 
condition  of  the  flowers  available.  On  June  1  and  July  6  no  bees  were 
attracted  to  the  honey,  while  on  April  30,  May  15,  June  15,  July  15,  and 
August  1,  the  respective  numbers  were  7,  3,  6,  7,  and  1.  On  August  15, 
13  bees  were  noted,  23  on  August  30,  a  host  on  September  16,  and  15  to  20 
on  the  30th.  The  most  striking  relation  was  the  inverse  one  to  the  number 
and  abundance  of  nectariferous  species  and  the  nectar  flow.  The  visitors 
to  the  honey  were  few  or  none  until  the  flowers  decreased  greatly  or  dis- 
appeared altogether,  when  they  increased  from  two  to  several  fold.  Zander 
regarded  the  observations  of  June  1  and  July  6  as  the  only  ones  that  sup- 
ported Forel's  view  as  to  the  bee's  feeble  sense  of  smell  for  honey,  but  it 
would  appear  that  all  the  observations  that  yielded  but  1  to  7  visits  should 
also  be  considered  as  evidence  for  this,  if  those  that  gave  20  to  many  vis- 
itors be  adduced  in  proof  of  a  keen  sense  of  smell.  Interesting  as  the 
experiments  are,  they  fail  to  reckon  sufficiently  with  the  effect  of  habit 
on  the  one  hand  and  the  tendency  of  bees  to  attract  others  on  the  other, 
to  be  entirely  conclusive.  They  do  show,  however,  that  the  sense  of  smell 
is  psychic  as  well  as  physical,  in  that  the  stimulus  of  the  odor  of  honey  is 
much  less  effective  in  the  midst  of  the  obsession  produced  by  an  abundant 
flow  of  nectar. 

The  sense  of  smell  in  the  honey-bee. — Frisch  has  supplemented  his 
studies  of  the  attraction  exerted  by  color  by  a  second  outstanding  research 
on  the  sense  of  smell  in  the  honey-bee  (1919:1).  As  this  likewise  became 
available  only  after  the  present  book  was  in  type,  it  must  suffice  to 
indicate  the  main  heads  of  his  treatment  and  to  give  the  essence  of  his 
summary.  The  main  divisions  of  his  treatise,  which  has  the  proportions 
of  a  book,  are  as  follows:  (1)  exposition  of  the  experimental  technique,  and 
discussion  of  the  question  whether  bees  are  attracted  by  the  odor  of  flowers; 
(2)  ability  of  the  honey-bee  to  discriminate  between  different  odors;  (3) 
odor  and  color;  (4)  memory  of  the  honey-bee  for  odor  and  color;  (5)  do 
scentless  inconspicuous  flowers  that  are  much  visited  by  bees  have  a  fra- 
grance imperceptible  to  us?  (6)  the  odor  of  honey;  (7)  the  fineness  of  the 
sense  of  smell  in  the  honey-bee  (the  "minimum  perceptibile ") ;  (8)  experi- 
ments with  mixed  odors;  (9)  the  biological  significance  of  the  fragrance  of 
flowers;  (10)  experiments  with  odorous  substances  of  different  chemical 
composition  but  similar  odor;  (11)  training  with  lysol,  skatol,  etc.,  a  con- 
tribution to  the  psychology  of  the  honey-bee;  (12)  summary. 

The  first  questions  to  be  decided  were  whether  the  honey-bee  perceives 
the  odor  of  flowers  and  whether  it  is  guided  by  such  perception  in  its  visits 
to  flowers.  The  answer  in  both  cases  is  affirmative,  since  training  for  flower 
odors  has  always  met  with  complete  success.  But  in  addition  to  odor 
itself,  its  quality  must  be  taken  into  account.  Bees  trained  to  the  fragrance 
of  acacia  visit  this  alone  and  are  not  in  the  least  attracted  by  the  odor  of 
the  rose  or  lavender.     Bees  trained  to  the  odor  of  the  oil  from  orange-peel 


204  PRINCIPLES  AND   CONCLUSIONS. 

distinguish  this  by  smell  from  43  other  essential  oils  with  the  greatest 
certainty,  and  are  attracted  only  by  a  similar  oil  of  different  origin  and  by 
bergamot  and  cedar  oils.  It  is  not  especially  noteworthy  that  the  essential 
oils  which  are  similar  to  our  sense  of  smell  should  be  the  very  ones  confused 
by  the  bees,  since  they  are  related  in  origin  and  chemical  composition. 
Comprehensive  experiments  with  paired  odorous  substances  of  different 
chemical  constitution  but  smelling  alike  to  us  have  shown  that  many  of 
them  are  also  confused  by  the  bee,  and  that  a  similar  grade  of  likeness 
appears  to  exist  also  for  it.  This  indicates  that  the  physiological  basis  of 
the  sense  of  smell  in  man  and  in  bees  has  more  in  common  than  has  pre- 
viously been  supposed  for  organs  that  are  anatomically  so  different.  How- 
ever, in  detail  the  two  show  considerable  departures.  Many  odorous  sub- 
stances, very  similar  to  us  but  easily  distinguishable,  were  mixed  by  the 
bees,  and  on  the  contrary  the  latter  distinguished  with  great  accuracy  others 
that  can  not  be  discriminated  by  us. 

When  bees  trained  to  both  odor  and  color  were  exposed  to  the  two  sepa- 
rately, the  behavior  was  complex,  but  it  was  regularly  the  case  that  the  color 
was  perceived  at  considerable  distances  and  the  odor  only  near  at  hand, 
even  when  strong  odors  were  borne  toward  the  bee  by  a  gentle  wind. 
This  and  other  observations  support  the  assumption  that  the  sense  of  smell 
in  bees  is  not  materially  keener  than  in  man.  It  might  be  supposed  that 
the  perception  of  odors  related  to  their  life  activities  would  be  greatly  en- 
hanced in  bees,  and  that  they  would  perceive  the  odor  of  nectar  or  honey 
at  great  distances.  However,  this  is  not  supported  by  the  results.  A 
honey  fragrance  that  is  little  or  not  at  all  perceptible  to  man  also  gives  no 
positive  results  with  bees.  With  a  stronger  honey  odor  an  actual  training 
can  be  effected,  but  the  observations  of  other  investigators  that  have  led 
to  the  assumption  of  its  attractive  effect  at  a  distance  can  be  otherwise 
explained.  The  honey  odor  is  probably  nothing  more  than  the  fragrance 
of  the  flower  that  has  been  absorbed  by  the  nectar,  and  it  is  understandable 
that  it  should  affect  the  bee  like  any  weak  fragrance  of  this  sort. 

Some  evidence  exists  for  the  assumption  that  many  flowers  which  are 
scentless  for  us  have  a  strong  odor  for  bees,  and  this  has  been  assumed  for 
the  wild  grape  especially.  However,  it  can  be  demonstrated  that  these 
flowers  have  just  as  little  odor  for  bees  as  for  us,  and  this  is  true  likewise  for 
the  bilberry  and  the  red  currant.  Outside  of  these  three  species  there  are 
but  few  whose  blossoms  are  both  inconspicuous  and  scentless,  and  yet 
visited  by  bees.  These  are  trees  or  shrubs,  or  plants  that  grow  in  extensive 
closed  masses,  with  the  consequence  that  they  are  easily  found  by  bees. 
The  experiments  with  mixed  odors  show  that  the  fragrance  of  scattered 
flowers,  even  when  marked,  can  be  effective  only  in  the  immediate  vicinity, 
where  it  is  pure  and  unmixed. 

While  fragrance  has  been  regarded  as  a  means  of  attracting  pollinators, 
this  is  not  wholly  correct;  at  least,  it  does  not  fully  characterize  its  function. 
When  a  bee  has  found  the  food  desired  in  a  particular  species,  it  brings  its 
companions  with  it  and  these  then  haunt  the  plant  with  great  persistence, 
distinguishing  it  with  the  greatest  assurance  from  all  others.  Inasmuch  as 
they  see  only  "yellow,"  "blue/'  and  white  flowers  out  of  the  entire  series  of 
shades,  they  must  make  use  of  other  characters  to  discriminate  between 


RECENT   INVESTIGATIONS.  205 

the  various  species.  Thus,  flower  fragrance  is  a  distinguishing  mark  for 
bees,  and  perhaps  the  most  important  one  that  the  flower  possesses.  In 
the  light  of  this  fact,  it  is  readily  understood  how  bees  can  remember  for 
days  or  even  weeks  an  odor  to  which  they  have  been  trained  for  a  short  time 
only. 

It  seems  significant  of  the  psychic  processes  in  these  highly  organized 
insects,  which  are  able  to  perceive  flower  odors  so  quickly  and  to  make  use 
of  them,  that  they  refuse  almost  completely  to  respond  to  training  experi- 
ments with  foul-smelling  substances,  and  that  certain  other  odorous  sub- 
stances give  only  poor  training  results.  There  seems  no  other  explanation 
of  this  than  the  assumption  that  there  are  odors  which  had  been  without 
significance  for  bees  through  countless  generations  and  to  which  they 
habituated  themselves  not  to  respond.  In  like  manner  they  readily  learn 
to  distinguish  forms  which  suggest  those  of  flowers,  while  training  them  to 
geometric  figures  is  completely  unsuccessful. 

In  their  entire  behavior  bees  show  in  their  sense  of  smell  an  agreement 
with  that  of  man  which  is  as  far-reaching  as  it  is  unexpected.  All  of  the 
32  odors  to  which  they  were  trained  are  effective  for  them,  as  for  us.  All 
the  substances  tested  that  are  inodorous  for  us  are  equally  so  for  them.  Sub- 
stances with  strong  odor  for  us  are  likewise  strong  for  bees  and  the  reverse, 
just  as  those  that  are  similar  for  the  one  are  alike  for  the  other.  Thus,  it 
is  possible  to  evaluate  the  biological  significance  of  flower  odors  with  far 
greater  certainty  than  heretofore. 

Bombylius  and  the  colors  of  flowers. — Knoll  has  presented  the 
results  of  his  investigations  of  the  behavior  of  Bombylius  and  Macroglossa 
in  two  comprehensive  monographs,  which  must  be  ranked  with  those 
of  Frisch  with  respect  to  the  detail  and  accuracy  of  the  treatment.  The 
first  deals  primarily  with  the  response  of  Bombylius  fuliginosus  to  the  flowers 
of  Muscari,  under  the  following  headings:  (1)  main  objects  of  the  experi- 
ments; (2)  experiments,  (a)  choice  and  preparation  of  the  experimental 
area,  (b)  determination  of  the  optical  attraction  of  flowers,  (c)  studies  of 
the  chemical  attraction  of  flowers,  (d)  experiments  with  Frisch's  methods, 
(e)  near-by  attraction  of  Muscari;  (3)  constancy  of  Bombylius  in  its  visits 
to  certain  flowers  and  the  behavior  of  other  species  of  the  genus  to  the  same 
flowers;  (4)  general  considerations  on  the  color  sense  of  Bombylius  and  that 
of  the  honey-bee.  The  experimental  results  showed  that  the  flowers  of 
Muscari  attracted  this  fly  at  a  distance  by  color  and  form  and  that  fragrance 
had  no  part  in  this.  It  was  also  found  that  Bombylius  possessed  the  ability, 
though  probably  in  smaller  degree  than  in  the  honey-bee,  to  associate  the 
color  of  a  flower  and  the  presence  in  it  of  an  easily  accessible  store  of  nectar. 
Further,  since  this  fly  visits  the  brightest  or  pure  white  flowers  as  well  as 
the  less  bright  ones  of  the  blue  group,  but  ignores  the  deep  yellow,  which 
are  also  very  bright,  it  seems  that  the  attraction  is  determined  by  the  quality 
of  the  color  rather  than  by  its  intensity.  It  may  be  assumed  that  the 
color  vision  of  insects  and  of  vertebrates  has  been  developed  independently 
on  the  basis  of  the  independent  evolution  of  the  sense  organs  and  the  related 
nerve  systems.  A  consideration  of  the  structure  of  the  sensory  apparatus 
and  the  central  organ  of  the  two  groups  confirms  us  in  the  assumption  that 


206  PRINCIPLES  AND   CONCLUSIONS. 

a  more  or  less  different  expression  of  physiologically  similar  functions  must 
result  from  organs  so  differently  constituted. 

As  a  consequence  of  what  has  been  said,  a  part  of  the  teaching  of  Sprengel 
as  to  the  ecological  significance  of  the  color  of  flowers  can  be  accepted  by 
modern  flower  biology  without  modification.  One  reservation  must  be  made, 
however,  to  the  effect  that  the  two  insects  so  far  investigated,  the  honey-bee 
and  the  bombyliad,  possess  a  different  optical  perception  of  what  appears 
to  us  as  pure  red  or  blue-green  in  color  and  that  in  consequence  neither  of 
these  colors  can  exert  an  attractive  action  on  these  insects  in  connection 
with  pollination.  However,  the  questions  as  to  the  nature  of  insect  vision 
and  the  ecological  significance  of  the  details  of  color  and  marking  in  flowers 
can  not  be  conclusively  answered  with  our  present  knowledge. 

Vision  and  flower  behavior  of  Macroglossa  stellatarum. — The  sec- 
ond half  of  Knoll's  monograph  on  insects  and  flowers  treats  of  the  response 
of  the  hawk-moth  to  light  and  color,  as  well  as  to  flowers,  under  the  follow- 
ing main  captions:  (1)  observations  on  the  life-history  of  Macroglossa;  (2) 
experiments  on  the  vision  of  Macroglossa;  (3)  the  food  instinct  in  Macro- 
glossa and  its  evaluation  for  the  study  of  the  color  sense;  (4)  experiments 
with  freshly  hatched  moths;  (5)  the  behavior  of  the  female  during  the  period 
of  egg  deposit;  (6)  flower  visits  and  fragrance;  (7)  critique  of  the  experi- 
ments of  Plateau  (p.  164);  (8)  notes  on  other  Lepidoptera;  (9)  summary. 

In  its  flights  for  nectar,  Macroglossa  observes  objects  of  a  certain  optical 
quality,  but  not  those  of  a  different  one.  In  addition  to  the  dark  colors, 
it  often  visits  also  the  paler  ones  and  pure  white,  but  takes  no  notice  of 
green  plant  parts,  and  just  as  little  of  the  gray,  black,  or  brown  objects  of 
its  environment.  With  the  hawk-moth,  as  with  the  honey-bee  and  the 
bombyliad,  two  groups  of  colors  come  into  especial  consideration,  namely, 
blue  and  yellow.  When  it  has  obtained  its  nectar  for  some  time  solely 
from  an  object  of  a  definite  optical  character,  under  certain  conditions 
there  appears  an  association  with  such  an  object.  In  the  attraction  of  this 
moth  from  a  distance  the  fragrance  of  flowers  plays  no  part,  as  this  appears 
to  be  true  also  for  the  immediate  proximity  of  the  flower.  This  result  was 
entirely  unexpected,  as  it  has  been  generally  assumed  in  flower  biology 
that  the  marked  fragrance  of  many  flowers  was  a  direct  adaptation  to  the 
hawk-moths.  However,  this  particular  species  does  not  lack  the  faculty  of 
perceiving  plant  odors,  since  the  odor  of  Galium  leads  the  female  to  deposit 
her  eggs  upon  it. 

A  newly  hatched  hawk-moth  flies  directly  to  certain  flowers,  in  spite  of 
the  fact  that  it  has  had  no  individual  experience  with  them.  In  doing 
this  it  distinguishes  the  color  of  the  blue  and  yellow  groups  from  green  and 
the  various  grays.  Thus,  there  is  present  in  the  inexperienced  moth  a 
predilection  for  objects  of  a  certain  optical  effect.  This  effect  is  given  in 
nature  only  by  flowers,  so  that  the  young  insect  may  go  quickly  to  its  food 
in  consequence.  The  action  of  certain  optical  stimuli  in  the  process  of 
flying  to  the  flowers  and  the  consequent  possibility  of  acquiring  experience 
by  means  of  vision  furnishes  the  basis  for  a  part  of  the  constancy  of  the 
hawk-moth.  This  utilization  of  animal  experience  has  already  been  made 
by  other  investigators  in  this  field,  notably  by  Frisch  with  the  honey-bee. 
A  comparison  of  the  results  shows  that  there  is  no  essential  difference  be- 


RECENT   INVESTIGATIONS.  207 

tween  the  color  sense  of  the  honey-bee  and  that  of  the  hawk-moth,  as  is 
equally  true  for  the  latter  and  Bombylius. 

Since  attraction  from  a  distance  is  a  matter  of  vision,  the  hawk-moth 
will  regularly  visit  only  those  flowers  that  belong  to  its  particular  color 
groups.  This  is  supported  by  the  records  of  visits,  which  show  that  the 
flowers  commonly  sought  are  blue  or  purple  in  color,  though  in  southern 
Europe  the  yellow  flowers  of  Linaria  vulgaris  may  be  exclusively  visited. 
This  difference  in  behavior  in  various  regions  may  be  regarded  as  a  passing 
stage  of  the  natural  association,  and  therefore  as  a  consequence  of  the  insect's 
experience.  To  effect  pollination  it  is  desirable  that  the  hawk-moth  visit 
the  flowers  of  one  species  for  as  long  a  period  as  possible.  Therefore,  all 
the  features  of  the  flower  are  of  significance  that  produce  and  fix  the  associ- 
ation of  the  moth  with  this  particular  species.  Of  paramount  importance 
in  this  are  those  optical  features  which  guide  the  moth  to  adequate  supplies 
of  nectar.  In  connection  with  such  optical  associations  the  nectar  guides 
may  play  an  important  role. 

The  above  results  confirm  in  large  measure  the  views  of  the  earlier 
flower  biologists  as  to  the  significance  of  the  optical  features  of  flowers  for 
the  visits  of  the  hawk-moth.  The  importance  of  nectar  guides  was  some- 
what overemphasized  by  them,  though  the  essential  facts  of  the  older  con- 
cept can  be  maintained.  However,  no  support  has  been  found  for  the 
view  that  the  odor  of  flowers  plays  the  important  part  in  the  attraction 
of  the  hawk-moth  heretofore  assigned  to  it. 

Response  of  bees  to  spectral  bands. — The  studies  of  Kuhn  and  Pohl 
(1921:738)  mark  a  distinct  advance  in  the  technique  employed  for  the 
analysis  of  color  vision  in  insects.  They  have  utilized  the  spectral  bands 
obtained  by  means  of  the  mercury  spectrum  in  order  to  extend  their  experi- 
ments into  the  region  of  the  ultra-violet  and  have  consequently  had  the 
advantage  of  working  with  pure  colors.  The  bees  were  habituated  to  fly 
in  a  room  in  which  a  Hg  spectrum  was  thrown  on  a  horizontal  table-top, 
upon  which  it  could  be  turned  and  shifted  at  will.  To  human  eyes  the 
lines  at  578  mm  (yellow),  546  (jl/jl  (green),  and  436  nn  (blue)  appeared  brilliant; 
405  ^n  (violet)  was  distinctly  and  492  nn  (blue-green)  still  noticeably  to  be 
seen  in  the  daylight  of  the  room.  The  line  365  nn  (ultra-violet)  could  be 
recognized  in  weaker  light  as  a  sensible  bluish  glow  on  the  white  paper  of 
the  table.  In  training  the  bees  all  the  lines  were  eliminated  except  one, 
which  was  directed  upon  a  small  elongated  combustion  dish  filled  with 
sugar  solution.  In  doing  this  the  position  of  the  line  was  frequently  shifted 
to  avoid  any  association  with  a  particular  portion  of  the  table.  In  the 
tests  without  food  a  new  sheet  of  paper  was  spread  and  the  particular  wave- 
length presented  in  proper  sequence  with  the  remaining  lines  of  the  spectrum. 
After  a  training  period  of  an  hour  the  bees  always  gave  a  constant  response. 

After  training  to  578  ixn  (yellow)  the  bees  concentrated  regularly  upon 
this  band.  When  this  was  covered,  they  went  in  almost  equal  number  to 
546  uti  (green).  Lines  of  shorter  wave-length  were  not  noticed,  and  varia- 
tions in  the  brightness  within  wide  limits  had  no  effect.  After  feeding  upon 
436  ij-h  (blue)  a  dense  mass  of  bees  formed  on  this;  violet  (405  nn)  was 
equally  strong  in  effect  after  uncovering  from  436  n/x.  After  eliminating 
436  nn  and  405  nn,  there  was  a  marked  movement  to  the  ultra-violet  line 


208  PRINCIPLES   AND   CONCLUSIONS. 

365  mm-  The  region  of  greater  wave-length  was  completely  avoided  after 
training  to  436  nn  and  405  nn.  The  wave-lengths  of  ca.  400  to  440  nn  on 
the  one  hand  and  ca.  540  to  580  nn  on  the  other  were  consequently  dis- 
criminated from  each  other  by  the  eyes  of  the  bee.  The  flight  to  the  ultra- 
violet line  365  fin  after  training  to  436  fifi  or  495  nn  (blue  or  violet)  may  be 
explained  by  the  action  of  the  weak  bluish  fluorescence  or  by  a  sensitivity 
of  the  bee's  eye  to  this  part  of  the  spectrum.  Further  studies  indicate  a 
particular  specific  sensitivity  to  ultra-violet.  When  trained  to  365  fifi,  the 
bees  sought  ultra-violet  alone  out  of  the  entire  spectrum,  and  even  after 
concealing  this  line,  blue  and  violet  were  without  effect.  Unbroken  light 
rays  received  no  visits,  but  the  interpolation  of  an  ultra-violet  filter  which 
cut  out  wave-lengths  above  400  fifi  and  removed  the  disturbing  influence 
of  whiteness  brought  about  many  visits.  Light-waves  in  the  region  of 
365  hijl,  or  ultra-violet,  were  distinguished  qualitatively  from  unrefracted 
light  as  well  as  from  the  regions  of  ca.  400  to  440  fifi  and  ca.  540  to  580  fifi. 
Further  experiments  showed  that  the  line  492  fifi  (blue-green)  was  also 
distinguished  from  the  other  lines  of  the  Hg  spectrum  as  well  as  from  unre- 
fracted light.  The  bees  were  then  trained  to  a  bright  band  from  a  continu- 
ous spectrum  between  480  fifi  and  500  fifi.  Checking  with  the  Hg  spectrum 
gave  a  massing  upon  the  blue-green  mercury  line  of  492  fifi,  which  is  faint 
to  our  eyes  and  which  always  remained  free  in  the  training  to  all  the  other 
wave-lengths.  In  order  to  test  the  discrimination  of  the  region  480  to  500  fifi 
from  unrefracted  light,  a  "white"  band  of  the  same  size  was  exposed 
alongside  of  or  instead  of  the  "blue-green"  one.  The  bees  left  this  un- 
noticed, even  though  its  brightness  was  varied  greatly,  and  gathered  always 
on  the  blue-green  strip  (480  to  500  fifi).  To  this  region  of  the  spectrum 
corresponds  Hering's  paper  No.  10  approximately  for  our  eyes.  In  the 
experiments  of  Frisch  the  bees  were  unable  to  distinguish  this  pigment  from 
the  shades  of  gray,  but  the  explanation  of  this  discrepancy  seems  obvious. 
Pigment  No.  10  has  been  measured  photo-electrically  and  found  to  reflect 
from  492  fi/i  to  365  fifi  downwards  in  increasing  measure.  Consequently, 
there  must  have  been  present  for  the  bee's  eyes  a  marked  veiling  by  white. 

EVALUATION  OF  PLATEAU'S  RESEARCHES. 

Forel's  estimate. — The  most  comprehensive  critique  of  Plateau's 
work  was  made  by  Forel  (1901,  1908:142).  As  a  complete  summary  of 
this  would  involve  too  much  repetition  of  Plateau's  results,  it  appears 
best  to  quote  Forel's  general  statements  and  conclusions,  and  to  deal  with 
certain  contradictions  which  affect  the  significance  of  some  of  his  criticisms. 

"It  is  with  reluctance  that  I  have  decided  to  undertake  the  criticism  of  this  author, 
not,  indeed,  that  it  will  be  difficult,  but  because  of  the  space  it  demands,  and  because 
it  is  painful  to  me  to  have  to  bring  to  light  the  false  conclusions  of  a  colleague  whose 
patience,  work,  honour,  and  good  faith  I  esteem.  But  the  considerable  confusion 
that  Plateau  has  thrown  on  the  question  which  occupies  us,  in  spite  of  and  in  part  by 
his  long  and  patient  researches,  and  the  fact  that  his  conclusions  have  been  accepted 
all  too  easily  by  certain  authors  who  consider  themselves  to  be  very  superior  to  all 
that  has  preceded  them,  demands  that  we  examine  the  matter  closely. 

"Before  starting,  I  must,  to  simplify  matters,  lay  down  in  anticipation  certain 
general  theses  at  which  I  have  long  arrived  and  which  agree  in  short  with  the  results 


EVALUATION  OF  PLATEAU'S  RESEARCHES.  209 

of  Darwin,  Romanes,  Lubbock,  and  all  investigators  who  have  gone  deeply  into  the 
psychology  of  insects.    But  these  theses  require  to  be  definitely  formulated. 

"  (a)  Granted  that  there  is  often  a  principal  directing  sense,  the  rule  is  nevertheless 
that  insects  combine  the  impressions  of  several  senses  for  their  own  guidance. 

"(b)  Attention  plays  a  considerable  part  in  the  manner  in  which  insects  guide 
themselves.  When  it  is  strongly  directed  toward  a  goal  or  object,  they  are  often 
profoundly  oblivious  of  everything  else,  somewhat  like  an  absorbed  savant  (bee 
eating  honey;  ants  fighting). 

"  (c)  The  memory  of  insects  varies  much  according  to  the  species.  It  is  connected 
with  various  sensory  impressions.  It  is  much  better  than  one  would  imagine  a  priori 
in  insects  with  complicated  instincts  and  especially  in  social  hymenoptera,  but  it  is 
extremely  weak  in  the  small-brained  forms. 

"(d)  As  Lubbock  and  H.  Mueller  have  shown,  impulse  plays  a  great  part.  At- 
tracted by  the  sensations  of  sight  or  of  smell  or  of  both  combined,  the  insect  ends  by 
fixing  its  attention  on  an  object  or  on  an  instinctive  coordinated  act,  connected  with 
a  purpose.  When  this  fact  is  accomplished  it  may  be  seen  to  repeat  its  journey  or 
other  instinctive  acts  with  a  rapidly  increasing  precision. 

"(e)  Insects  have  sentiments  or  emotions  more  or  less  developed  according  to  the 
species,  genera,  and  families.  Rage,  fright,  discouragement,  jealousy  are  very  marked 
among  the  social  hymenoptera;  similarly  affection  and  temerity  based  on  success. 
It  is  necessary  to  take  them  into  account  accurately  to  judge  their  acts.  Emotional 
states  of  the  nerve  centers  are  very  general  in  the  animal  series  and  are  therefore 
related  to  danger,  success,  defeat,  fruitless  efforts,  pain,  attack,  defence,  as  much  in 
the  individual  as  in  the  society. 

"  (/)  Nothing  is  so  dangerous  as  premature  generalizations,  or  (g)  to  draw  illegitimate 
conclusions  from  experiments." 

"Attraction  of  insects  by  flowers. — Color  preferences. — It  is  well  known  that 
Hermann  Mueller  has  insisted  on  the  part  played  by  the  colors  of  flowers  as  a  cause  of 
attraction,  and  has  upheld  the  opinion  that  certain  lively  colors  of  flowers  of  themselves 
attract  insects,  i.  e.,  that  the  attraction  for  such  and  such  a  lively  color  will  tend  to 
direct  the  insect  towards  them  rather  than  towards  less  apparent  colors.  These 
preferences  of  color  thus  serve  indirectly  for  the  fertilization  of  flowers  by  insects, 
so  that  selection  will  induce  the  flowers  for  this  reason  to  become  more  and  more 
colored.  Lubbock  has  made  experiments  whence  it  resulted  that  bees  and  bumble- 
bees had,  for  example,  a  marked  preference  for  blue.  Let  us  say  once  for  all  that  this 
question  is  extremely  complex,  and  that  the  results  of  observations  made  without 
prejudice  are  not  of  a  nature  to  confirm  in  a  satisfactory  manner  the  theories  of  Mueller. 
The  results  of  Lubbock  are  similarly  not  very  conclusive  on  this  point.  It  has  often 
appeared  to  me  also  that  blue  was  especially  apt  to  attract  and  to  direct  bees  and 
bumble-bees  to  a  spot;  they  find  honey  placed  on  blue  more  easily,  for  example,  than 
if  on  red.  But  as  insects  distinguish  the  colors  on  the  side  of  the  ultra-violet  better 
than  those  on  the  side  of  the  infra-red,  the  preference  might  thus  be  accounted  for. 
White  attracts  them  in  my  opinion  as  much  as  blue,  everything  else  being  equal. 
In  this  question,  distinction  of  colors  must  not  be  confounded  with  preference  for  one 
or  another  color.  Though  the  distinction  of  colors  is  useful  to  insects  which  visit 
flowers,  to  enable  them  to  distinguish  and  find  them  rapidly,  the  attraction  of  a  special 
color  will  be  equally  detrimental  to  them  in  preventing  them  from  going  to  flowers 
quite  as  rich  in  nectar  or  pollen,  but  differently  colored,  or  in  attracting  them  toward 
flowers  or  other  objects  colored  with  the  hue  of  predilection,  but  offering  neither 
nectar  nor  pollen,  or  even  having  poisonous  qualities.  For  these  simple  reasons, 
self-evident  to  the  common-sense  of  a  practical  entomologist,  I  have  never  been  able 
to  participate  in  the  theories  of  Mueller  and  Lubbock  on  this  subject. 

"I  am  happy  to  find  myself  in  perfect  agreement  with  Plateau  on  this  point;  his 
numerous  experiments  all  tend  to  prove  clearly  what  would  be  expected,  i.  e.,  that 


210  PRINCIPLES   AND   CONCLUSIONS. 

insects  direct  themselves  toward  flowers  which  provide  them  with  the  nourishment 
that  they  need,  and  that  they  find  them  as  well  when  they  are  as  green  as  the  leaves, 
as  when  they  are  blue,  red,  or  yellow.  Inversely,  they  ignore  the  most  beautiful 
flowers  with  striking  colors,  when  these  have  nothing  to  give  them.  Plateau  gives 
himself  unnecessary  trouble  to  show  that  there  are  green  flowers  and  that  insects 
visit  them  as  much  as  others.  Every  one  knows  the  first  of  these  facts,  and  the  second 
has  escaped  no  entomologist;  in  my  opinion,  his  long  comparative  tables  refute  Mueller. 
Nevertheless,  do  there  exist  any  preferences  of  color  beside  the  fundamental  fact 
that  we  have  enunciated?  This  is  so  difficult  and  so  delicate  to  decide  that  I  dare  not 
express  an  opinion. 

"But  Plateau  has  completed  his  old  experiments  on  another  very  interesting  point. 
I  refer  to  artificial  flowers.  He  has  taken  enormous  trouble  to  obtain  the  best  and  most 
artistic  imitations  of  natural  flowers.  To  one  who  knows  modern  art  in  this  branch 
this  means  much,  for  even  man  needs  all  his  attention  to  enable  him  to  distinguish 
these  artificial  products  from  true  flowers.  Here  again  I  am  pleased  to  be  able  to 
confirm  Plateau  by  several  experiments  that  I  have  been  able  to  make.  That  which 
deceives  us  never  deceives  insects,  or  hardly  ever,  and  then  only  for  an  instant.  The 
insect  passes  to  one  side  of  artificial  flowers  without  paying  them  attention,  without 
stopping  at  them,  without  hesitating,  and  goes  straight  to  natural  flowers  situated 
beside  them,  and  which  we  do  not  distinguish  from  them.  Ought  we  to  conclude 
therefrom  that  the  colors  which  we  use,  and  which  are  not  chlorophyllic,  are  dis- 
tinguished by  insects  from  chlorophyllic  colors?  This  appears  very  probable  from 
Plateau's  experiments,  and  I  shall  believe  it  until  I  have  proof  to  the  contrary.  That 
which  to  our  eyes  is  a  good  imitation  of  color  appears  not  to  be  so  to  the  insect  eye. 
These  facts  will  appear  less  astonishing  to  us  if  we  remember  that  among  men  some 
are  color-blind,  while  others  are  artists  who  render  and  appreciate  colors  in  many 
various  shades.  Then  we  must  not  forget  that  artificial  imitations  of  flowers  are  made 
by  the  help  of  human  vision  and  for  it. 

"I  shall  not  enlarge  upon  the  researches  of  Mueller,  Bennett,  Bonnier,  Gratacap, 
Christy,  Bulman,  Scott  Elliot,  Delpino,  Kuntze,  Knuth,  and  Plateau  on  the  truly  hair- 
splitting question  regarding  the  possibility  of  insects  having  preferences  for  certain 
colors  or  not.  Here  I  am  in  agreement,  as  I  have  said,  with  Plateau  (and  Bulman). 
What  is  astonishing  is  that  so  many  authors  can  waste  so  much  ink  in  proof  of  the 
obvious,  clearly  summed  up  by  Bulman  when  he  saj^s,  'It  matters  not  one  iota  to 
a  bee  whether  the  flower  is  blue,  red,  pink,  yellow,  white,  or  green,  so  long  as  there  is 
honey,  that  is  sufficient.'  Only  the  fact  that  any  color  does  not  attract  specially  by  itself 
some  insect  is  no  proof  that  the  latter  cannot  distinguish  other  colors. 

"But  here  my  agreement  with  Plateau  ceases.  Here  again  he  has  drawn  erroneous 
conclusions  from  his  experiments.  In  the  case  of  masked  dahlias,  he  concludes  that 
shape  and  color  do  not  attract,  but  forgets  that  the  insect  remembers  the  place  where 
the  flower  was.  Plateau's  observations  and  inferences  are  both  faulty.  First,  his 
dahlias  were  insufficiently  masked,  being  covered  only  in  the  upper  part;  bees  flying 
around  a  group  of  flowers  must  perceive  the  uncovered  colored  sides  by  their 
peripheral  vision.  This  seems  to  be  evident  from  the  figures  of  Plateau,  which 
shows  the  vine  leaf  lying  flat  on  the  flower.  In  the  second  place  his  bees  had  conse- 
quently discovered  his  trick  sooner  than  mine;  he  probably  took  no  account  of  their 
behavior  at  the  beginning  of  his  experiment,  or  had  not  noted  it.  But  it  is  only  at 
such  a  time  that  conclusions  can  be  drawn  as  to  vision  alone,  independently  of 
memory.    Further,  our  results  show  that  bees  have  a  poor  sense  of  smell  at  a  distance. 

"Plateau  also  worked  with  bees  that  were  visiting  Oenothera  biennis  with  its  beautiful 
yellow  petals.  On  September  3rd  he  cut  the  corollas,  leaving  only  the  stamens. 
I  give  the  results  in  his  own  words: — 'The  bees  visiting  the  plant  flew  in  every  direction, 
toward  the  faded  flowers,  towards  the  buds,  even  to  the  fallen  petals  on  the  ground, 
which  they  examined  with  some  attention  in    walking  over    them;  nevertheless, 


EVALUATION  OF  PLATEAU'S  RESEARCHES.  211 

they  alighted  to  forage  only  on  the  mutilated  blossoms  deprived  of  corollas.'  [The  italics 
are  Plateau's!]  And  Plateau  concludes  that  it  is  smell  and  not  vision  that  guided 
them!  Is  it  possible  to  prove  better  to  oneself  the  contrary  of  what  his  experiment 
says?  That  bees  do  not  forage  where  there  is  nothing,  is  obvious  to  a  child.  But 
that  they  should  seek  the  flowers,  wherever  they  perceived  them,  by  their  bright 
yellow  color,  that  they  should  see  the  dry  rudiments  or  the  buds  on  the  plant,  this 
agrees  so  admirably  with  our  experiments  that  I  pass  no  comment. 

"The  last  conclusions  of  Plateau  are  somewhat  curious.  He  begins  by  declaring 
that  he  has  'never  said  that  insects  do  not  see  the  colors  of  flowers;  that  would  be 
absurd'  (jievertheless,  he  uses  the  title:  On  the  so-called  distinction  of  colors  by  insects). 
Then  he  adds  that  the  differences  in  the  quantities  of  reflected  light  or  in  the  refran- 
gibility  of  luminous  rays  transmitted  or  reflected  by  the  transparent  media  can  explain 
the  results  hitherto  obtained.  And  finally  he  pretends  that  the  question  to  be  solved 
U:  do  the  insects  which  visit  flowers  allow  themselves  to  be  guided  in  their  choice 
by  the  colors  which  these  flowers  present  to  the  human  eye?  I  protest  against  the  man- 
ner in  which  Plateau  now  puts  the  question.  I  do  not  believe  any  more  than  he  does 
that  insects  see  colors  subjectively  as  we  do,  and  I  believe  further  with  him  that  there 
are  objective  differences  in  the  manner  in  which  their  eyes  and  ours  are  stimulated 
by  the  different  forms  of  light,  i.  e.,  by  colors  and  shades.  But  the  experiments  of 
Lubbock,  of  Peckham,  of  other  authors,  and  my  own  indicate  that  certain  insects 
distinguish  not  only  flowers,  but  colored  objects,  by  their  coloration,  i.  e.,  by  the  kind 
of  refrangibility  of  the  luminous  rays  which  they  reflect  or  transmit,  and  recognize 
them  in  this  particular  when  the  other  senses  are  eliminated,  and  even  when  such 
objects  are  found  surrounded  by  light  of  the  same  intensity. 

"In  saying  that  bees  distinguish  colors,  We  have  never  wished  to  assume  that  they 
see  them  exactly  as  man  does,  and  so  much  the  less  since,  as  I  have  already  emphasized, 
all  men  do  not  see  them  absolutely  the  same. 

"In  recapitulation,  we  see  that  the  facts  are  very  complex,  and  this  is  why  I  abstain 
from  general  conclusions  on  'all  insects'  seeing  or  not  seeing  'forms  and  colors,  etc.,' 
for  such  generalization  would  necessarily  be  false.  If  one  wishes  to  understand  it, 
one  must  take  the  trouble  to  follow  the  details.  Nevertheless,  I  am  constrained  to 
repeat  that  Plateau's  interpretation  of  his  so-called  non-distinction  of  forms  among 
insects,  after  the  restrictions  which  he  has  himself  gradually  introduced,  finally 
approaches  more  or  less  to  the  opinion  of  Exner,  which  has  always  agreed  with  my 
own.  The  greatest  error  of  fact  into  which  Plateau  falls,  is  that  by  which  he  attributes 
what  really  belongs  to  vision  in  certain  insects  (in  bees  in  particular)  to  their 
sense  of  smell.  Nevertheless,  in  the  final  paper  of  the  series,  he  finally  recapitulates 
the  way  insects  guide  themselves,  in  a  manner  which  in  its  general  characteristics 
approaches  nearly  to  the  truth.  As  we  have  seen,  the  causes  of  the  erroneous  judg- 
ments with  which  Plateau  has  obscured  the  question  at  issue  are  errors  of  interpreta- 
tion, inadmissible  and  continual  generalizations,  and  the  almost  total  neglect  of  the 
psychical  faculties  of  the  insect,  especially  with  regard  to  memory  and  association." 

Although  Forel's  criticisms  of  Plateau's  work  are  often  too  severe, 
they  are  on  the  whole  fairly  well  justified.  They  err  in  making  the  dif- 
ferences between  their  general  conclusions  greater  than  it  actually  was, 
as  Plateau  himself  pointed  out  (19022:424).  Moreover,  Forel  was  not 
free  from  the  contradictions  for  which  he  takes  Plateau  to  task,  and  it 
is  evident  that  his  own  knowledge  of  the  behavior  of  anthophilous  in- 
sects was  much  smaller  than  for  many  other  groups.  After  dismissing 
the  views  of  Mueller  and  Lubbock  on  color  preference  as  unsatisfactory 
or  inconclusive,  he  states  that  "this  problem  is  so  difficult  and  delicate 
to  decide  that  I  dare  not  express  an  opinion,"  only  to  express  a  very  positive 


212  PRINCIPLES  AND   CONCLUSIONS. 

one  a  moment  later  (p.  210)  and  to  rebuke  Mueller,  Plateau,  and  others 
for  proving  the  obvious.  He  is  far  from  clear  as  to  the  practical  difference 
between  the  distinction  of  colors  and  the  preference  for  certain  ones,  and 
fails  to  realize  that  the  marked  constancy  of  many  bees  indicates  that 
distinction  and  preference  are  often  the  same  thing.  He  apparently  did 
not  know  the  careful  work  of  Mueller  as  to  color  preferences  for  petals, 
which,  like  that  of  Lubbock,  is  corroborated  by  the  later  researches  of 
Lovell,  Turner,  Frisch,  and  others.  Lovell  in  particular  has  shown  that 
green  flowers  and  green  objects  are  visited  much  less  than  bright-colored 
ones  and  often  not  at  all,  and  this  has  been  confirmed  by  Allard  in  his  work 
with  cotton  blossoms.  The  results  of  Plateau  and  of  Forel  with  respect 
to  artificial  flowers  are  contradicted  by  those  of  Andreae,  Wery,  Detto, 
and  others,  and  it  is  evident  that  time,  place,  and  other  factors  often 
play  a  controlling  part  in  the  behavior  of  insects  to  such  imitations.  Move- 
over,  if  insects  can  distinguish  chlorophyllic  colors  from  others  in  the  case 
of  artificial  flowers  that  deceive  human  vision,  it  is  impossible  to  believe 
that  they  are  unable  to  distinguish  the  strikingly  different  forms  of  various 
flowers.  The  evidence  for  the  perception  of  form  by  bees  is  given  later, 
and  it  is  only  necessary  to  point  out  here  that  Forel  himself  speaks  of  their 
seeing  the  dry  remains  of  flowers  and  the  buds  of  Oenothera. 

Contradictory  nature  of  Plateau's  later  conclusions. — While  several 
critics  have  pointed  out  that  Plateau  materially  modified  his  earlier  state- 
ments as  to  the  relative  r61e  of  color  and  odor  in  attraction,  the  greater 
contradictions  involved  in  his  later  ones  have  been  overlooked.  These 
are  contained  in  the  four  extracts  that  follow,  which  represent  the  last 
ten  years  of  his  work,  1899  to  1910. 

"I  have  never  said,  in  my  previous  studies  or  the  present  memoir,  that  insects  do  not 
see  the  colors  of  flowers.  This  assertion  would  be  absurd.  But  I  insist  that  we  have  no 
practical  means  of  assuring  ourselves  whether  there  exists  a  perception  of  color  and 
whether  this  is  the  same  as  our  own.  The  question  to  be  resolved  is  this:  whatever 
may  be  the  visual  perceptions  of  insects,  are  those  that  visit  flowers  guided  in  their  choice 
by  the  colors  that  the  flowers  present  to  the  human  eye.  The  reply  can  only  be  negative 
[1899:368].  I  admit  fully  that  the  insect  can  perceive  flowers  at  some  distance, 
whether  it  be  because  he  sees  their  colors  in  the  same  manner  that  we  do  or  because 
he  perceives  a  certain  contrast  between  the  flowers  and  their  surroundings,  I  admit 
that  concurrently  with  the  sense  of  smell,  although  to  a  much  less  degree,  this  vague 
visual  perception  can  guide  the  animal  to  the  whole  floral  mass;  but  once  arrived 
there,  if  the  flowers  differ  among  themselves  by  color  alone,  he  will  prove  by  his  be- 
havior that  it  is  entirely  indifferent  to  him,  as  Bulman  says,  whether  the  corollas  are 
blue,  red,  yellow,  white,  or  green"  (370). 

As  a  result  of  his  experiments  with  bumble-bees  deprived  of  their  an- 
tennae (1902*: 418),  Plateau  said: 

"The  results  of  A.  Forel  are  thus  shown  to  be  accurate;  I  state  it  with  the  satis- 
faction of  having  been  able  to  contribute  to  the  demonstration  of  a  scientific  truth. 
However,  it  is  not  necessary  to  draw  from  this  the  exaggerated  conclusion  that  the 
sense  of  smell  plays  no  part  in  the  attraction  of  insects  by  flowers."  "What  is  to  be 
drawn  as  a  conclusion  from  all  this?  It  is  that,  if  I  have  been  wrong  in  attributing 
an  exaggerated  preponderance  to  the  sense  of  smell  in  the  relations  between  insects 
and  flowers,  my  numerous  observations  and  experiments  prove,  as  Knuth  admitted, 
that  the  olfactory  sense  plays  a  much  more  important  r61e  in  the  search  for  flowers 
by  insects  than  has  hitherto  been  admitted. 


SENSES  of  insects:  sight  213 

"I  could  quote  further  from  the  work  of  Forel,  but  limit  myself  to  the  preceding. 
I  thank  him  for  giving  me  the  opportunity  to  prove  that,  even  in  supposing  all  the 
criticisms  of  which  he  is  not  sparing  to  be  absolutely  well  founded,  the  results  of  my 
studies  on  the  relations  between  insects  and  flowers  are  not  as  worthless  as  some  pre- 
tend and  that  they  do  lead  to  the  refutation  of  this  part  of  the  floral  theory  of  Hermann 
Mliller  and  his  school,  who  attribute  to  the  brilliance  of  flowers,  to  their  colors  more 
or  less  striking,  an  important  role  in  the  attraction  of  insects  and  consequently  in 
fecundation  (1902:424). 

"Two  corollaries  may  be  derived  from  this  fact:  the  first  is  that  the  attractive 
r61e  of  the  form  and  color  of  the  floral  envelopes  is  either  null  or  nearly  so;  the  second 
is  that  other  causes  than  the  attraction  of  colored  surfaces  is  necessary  to  bring  pol- 
linators to  flowers  and  to  cause  them  to  return,  such  as  an  odor  pleasing  to  insects 
and  a  sugary  liquid."  "In  r6sum£,  the  present  investigation  but  confirms  the  thesis 
advanced  in  1897  in  the  following  words:  'Insects  seeking  pollen  or  nectar  are  guided 
to  the  flowers  that  contain  these  substances  in  only  a  subordinate  degree  by  sight. 
They  are  guided  in  an  assured  manner  to  such  flowers  by  some  other  sense  than  vision 
and  this  can  only  be  the  sense  of  smell'  "  (1910:51). 

Conclusions  as  to  Plateau's  views. — The  admiration  felt  for  Plateau's 
frank  admission  that  he  had  been  wrong  in  assigning  an  exaggerated  im- 
portance to  the  sense  of  smell  in  attraction  is  more  or  less  eclipsed  by  the 
fact  that  this  was  never  again  referred  to  in  his  later  papers,  in  which 
he  returned  finally  to  his  original  view  that  the  attractive  role  of  color 
is  null  or  nearly  so.  In  spite  of  Plateau's  originality,  industry,  and  patience, 
the  bias  in  favor  of  odor  and  against  color  pervaded  all  his  researches, 
blinding  him  to  many  faults  of  execution  and  leading  him  to  unwarranted 
conclusions.  How  dominant  this  prejudice  was  is  shown  by  the  fact  that 
within  six  pages  after  his  apology  for  exaggerating  the  r61e  of  smell  in  at- 
traction, he  states  that  his  studies  refute  the  view  of  Mueller  that  color 
plays  an  important  part  in  this  process.  This  also  led  him  frequently 
to  overlook  facts  and  results  that  were  not  in  accord  with  his  views,  and  to 
make  gratuitous  assumptions  as  to  the  work  of  other  investigators.  A 
second  great  fault  of  his  experiments  was  the  failure  to  insist  upon  the 
regular  use  of  controls,  with  the  consequence  that  the  results  were  often 
open  to  any  interpretation  desired.  With  this  went  the  failure  to  realize 
that  time,  place,  and  conditions  work  great  differences  in  response,  and 
that  this  was  usually  the  explanation  of  the  discrepancies  between  his 
results  and  those  of  his  critics,  rather  than  carelessness  or  lack  of  thought 
on  their  part.  Finally,  as  Forel  in  particular  insisted,  he  paid  practically 
no  attention  at  first  to  the  importance  of  habit  and  memory,  and  gave 
them  too  little  consideration  throughout.  In  spite  of  all  this,  he  deserves 
great  credit  as  the  pioneer  in  experimental  pollination,  as  an  indefatigable 
investigator,  and  a  good-natured  and  courteous  opponent. 

SENSES  OF  INSECTS. 
SIGHT. 

The  mosaic  theory. — Forel  (1886:10)  emphasized  the  fact  that  the 
structural  studies  of  Grenacher  (1874)  and  the  physiological  ones  of  Exner 
(1875)  led  them  to  revive  the  earlier  theory  of  Muller.  This  was  not 
that  each  facet  formed  an  image,  as  Gottsche  thought  to  have  demon- 
strated, but  that  the  insect  perceives  a  more  or  less  clear  image  of  the 


214  PRINCIPLES   AND   CONCLUSIONS. 

object  in  the  form  of  a  mosaic,  due  to  the  fact  that  each  facet  receives  a 
different  part  of  the  light  rays  coming  from  the  object.  It  follows  necessarily, 
as  Muller  pointed  out,  that,  since  the  clearness  of  vision,  the  localization 
of  the  light  rays,  is  rendered  possible  only  by  the  combination  of  the  separate 
action  of  each  facet,  it  is  the  number  of  facets  that  will  determine  the 
degree  of  definition.  The  smaller  the  facet,  the  longer  the  crystalline,  the 
fewer  the  rays  the  retinule  will  receive  and  the  smaller  or  more  localized  will 
be  the  external  object  from  which  the  rays  proceed.  On  the  contrary,  the 
larger  the  facet  and  the  shorter  the  crystalline,  the  more  light  the  retinule 
will  receive  and  it  will  see  in  a  manner  more  intense  and  diffuse,  that  is,  less 
clearly.  Thus,  many  small  facets  will  diminish  the  intensity  of  the  light, 
but  will  increase  the  clearness  of  vision.  When  in  addition  the  entire  eye 
is  not  flat  but  strongly  convex,  it  will  receive  light  from  more  diverse 
points,  which  increases  the  common  field  of  vision.  If  this  be  true,  it  ought 
to  be  possible  to  prove  by  observation  that  insects  with  many  small  facets 
and  with  the  compound  eyes  strongly  convex  have  the  best  vision. 

Forel  brought  forward  a  number  of  observations  to  support  this  view, 
the  most  significant,  perhaps,  being  with  reference  to  eyes  of  male  and  female 
ants.  The  eyes  of  the  former  are  more  convex  and  may  contain  twice 
as  many  facets,  since  they  require  greater  vision  to  discern  and  follow 
the  females  in  flight.  He  also  confirmed  the  opinion  of  many  investigators 
that  the  loss  of  the  ocelli  was  without  effect,  but  that  this  was  not  the  case 
with  the  compound  eyes.  When  the  latter  were  varnished  in  the  case  of 
flies,  these  no  longer  flew  if  placed  on  the  ground  and  once  in  the  air  they 
flew  about  aimlessly.  Wasps  and  bumble-bees  similarly  treated  behaved 
in  like  manner,  flying  even  more  rarely  and  finding  their  way  on  the  ground 
more  slowly.  They  searched  for  cracks  in  which  to  hide,  as  though  it 
were  night. 

The  following  summary  was  given  of  the  existing  knowledge  of  vision 
in  insects. 

1.  Insects  guide  themselves  almost  wholly  in  flight  and  partly  on  the  ground  by 

means  of  their  compound  eyes.  The  antennae  and  the  sensory  organs  of 
the  mouth  can  not  serve  for  direction  in  the  air,  their  extirpation  in  no  wise 
diminishing  the  ability  to  guide  themselves  on  the  wing. 

2.  The  mosaic  theory  of  vision  proposed  by  Muller  is  alone  sound.    Each  retinule 

of  the  compound  eye  does  not  receive  an  image,  but  merely  a  pencil  of  light 
rays  more  or  less  distinct  from  that  of  its  neighbors. 

3.  The  greater  the  number  of  facets  and  the  length  of  the  crystallines,  the  more  dis- 

tinct the  sight,  as  well  as  further. 

4.  Insects  perceive  the  movements  of  objects  particularly  well,  that  is,  the  displace- 

ments of  the  visual  image  relative  to  the  compound  eye.  They  thus  see  better 
in  flight  than  at  repose,  for  the  image  of  immobile  objects  is  then  displaced 
with  respect  to  the  eye.  Perception  of  the  mobility  of  objects  decreases  as  the 
distance  becomes  greater. 

5.  Insects  distinguish  the  contours  and  form  of  an  object  only  in  a  manner  more  or 

less  indistinct,  as  much  more  indistinct  as  the  number  of  facets  is  less,  the  crys- 
tallines shorter,  the  object  more  distant  or  smaller.  Those  insects  that  have 
large  eyes  with  several  thousand  facets  see  quite  distinctly. 

6.  In  flight  insects  recognize  the  direction  and  distance  of  objects  very  clearly  by 

means  of  their  compound  eyes;  at  least  this  is  true  for  short  distances.  Even 
when  in  repose  they  can  also  recognize  the  distance  of  immobile  objects. 


SENSES  of  insects:   sight  215 

7.  Certain  insects,  the  honey-bee  and  bumble-bee,  clearhy  distinguish  colors  and  they 
recognize  colors  better  than  forms.  With  the  wasps  on  the  contrary  the  per- 
ception of  colors  appears  to  be  very  rudimentary. 

Criticisms  of  Plateau's  views  as  to  vision. — Forel  stated  (p.  43)  that — 

"Plateau  began  by  assuming  that  the  theory  of  Muller  as  to  mosaic  vision  is  finally 
rejected  and  this  in  consequence  of  the  work  of  Exner  of  which  we  have  spoken! 
This  is  completely  in  error.  On  the  contrary  we  have  seen  that  Exner,  as  well  as 
Grenacher,  has  entirely  rehabilitated  the  theory  of  Muller.  Plateau  appears  to  have 
failed  to  understand  the  works  of  Exner,  because  he  also  adds  that  this  author  has 
concluded  theoretically  that  insects  do  not  see  the  form  of  objects,  which  is  wholly 
inexact  as  well.  Plateau  says  in  the  text,  'The  earlier  hypothesis  of  J.  Muller,  con- 
sisting in  the  production  of  a  mosaic  image  formed  by  the  juxtaposition  of  a  series 
of  minute  partial  images  each  of  which  occupies  the  base  of  one  of  the  distinct  elements 
of  the  compound  eye  is  definitely  rejected.'  But  this  is  the  theory  of  Gottsche  and  not 
at  all  that  of  mosaic  vision  of  Muller.  The  theory  of  mosaic  vision  does  not  admit 
of  minute  images  in  each  facet,  but  a  single  image  in  mosaic  formed  by  the  juxta- 
position of  light  rays  of  different  quality  perceived  by  each  facet." 

As  to  the  experiments  of  Plateau  upon  the  perception  of  form  by  in- 
sects, Forel  declared  that  these  did  not  in  the  least  demonstrate  that 
they  could  not  distinguish  form,  but  merely  that  they  would  fly  to  the 
more  luminous  of  the  two  orifices  without  regard  to  the  form.  He  also 
pointed  out  that  while  Plateau  first  spoke  only  of  the  non-perception 
of  form,  he  concluded  by  saying  that  "insects  do  not  distinguish  the 
form  of  objects  or  distinguish  it  very  badly." 

Sensibility  to  color. — Graber  said  (1875): 

"I  understand  very  well  that  a  brain  relatively  small  and  simple  in  construction 
is  in  general  less  capable  than  a  more  highly  differentiated  central  organ  and  that 
both  the  number  and  the  coordination  of  perceptions  is  limited  by  the  simplicity  of 
structure,  but  I  can  not  admit  offhand  that  when  an  animal,  let  us  say  a  bee  for  ex- 
ample, exhibits  actual  color  perceptions,  these  must  necessarily  be  different  from  ours, 
or  that  we  then  know,  since  the  sensory  organ  for  color  perception  in  the  bee  is  essen- 
tially different  than  with  us,  that  the  nerve  tissues  concerned  can  not  call  forth  the 
same  sensations  that  they  do  with  us.  Disregarding  the  fact  that  insects  possess 
very  complex  eyes  and  that  they  appear  to  react  clearly  to  small  differences  of  color, 
such  as  orange,  yellow-green,  etc.,  other  evidence  testifies  to  the  great  sensibility  of 
their  sense  of  color.  I  have  especially  in  mind  the  fact  that  many  insects  have  no 
other  means  of  recognizing  their  own  species  than  certain  differences  in  color  and  it 
is  well  known  that  related  species  often  differ  outwardly  only  in  coloring  or  marking. 
Moreover,  it  is  hardly  to  be  assumed  that  mutual  recognition  takes  place  by  means  of 
other  attractions,  imperceptible  to  us,  such  as  odor  or  sound.  But  if  I  ascribe  a  very 
delicate  sense  of  color  to  certain  insects  on  the  basis  of  these  relations,  I  do  not  how- 
ever go  so  far  as  Allen,  who  asserts  that  the  ability  of  insects  to  distinguish  color 
may  be  more  marked  than  with  man." 

Perception  of  form  and  movement  by  insects. — In  a  series  of  six 
papers  appearing  from  1885  to  1888,  Plateau  dealt  with  a  comprehensive 
investigation  of  vision  in  the  Arthropoda.  Some  of  these  were  made  upon 
other  groups  than  the  insects  and  others  had  little  or  no  relation  to 
the  problem  of  insect  attraction.  In  consequence,  the  following  account 
of  his  conclusions  is  confined  to  those  that  have  to  do  with  the  perception 
of  form  or  movement.    Diurnal  insects  require  a  fairly  strong  light  and 


216  PRINCIPLES  AND   CONCLUSIONS. 

are  unable  to  direct  themselves  in  semi-obscurity.  Insects  with  com- 
pound eyes  pay  no  heed  to  differences  of  form  existing  between  two  illum- 
inated openings  and  are  deceived  either  by  excess  of  luminous  intensity 
or  of  apparent  surface.  In  short,  they  do  not  distinguish  the  forms  of 
objects  at  all,  or  do  so  very  poorly  (1885:251). 

Plateau  (1888:437)  stated  that  Exner,  Notthaft,  Carriere,  Forel,  and 
Bleuler  had  all  concluded  from  theoretical  considerations,  often  sup- 
ported by  observations,  that  the  majority  of  insects  see  the  movements 
of  bodies  much  better  than  they  do  the  bodies  themselves.  He  regarded 
his  own  experiments  as  fully  confirming  this  opinion  and  permitting  the 
following  conclusions.  The  faculty  of  perceiving  the  displacement  of 
mobile  objects  is  very  well  developed  in  many  insects  with  compound 
eyes,  those  best  endowed  in  this  respect  being  the  Lepidoptera,  Hymen- 
optera,  Diptera,  and  Odonata.  However,  the  distance  at  which  the  move- 
ments of  an  object  of  small  volume  are  perceived  does  not  exceed  2  meters. 
On  the  average  it  is  1.5  meters  for  the  butterflies,  58  cm.  for  the  bees,  and 
68  cm.  for  the  flies.  The  perception  of  movement  plays  a  great  r61e  as 
the  determining  cause  in  the  behavior  of  insects.  It  explains  how,  with- 
out a  clear  vision  of  form,  the  dragon-flies  pursue  their  victims  in  the 
air,  how  different  insects  fly  about  among  leaves  moved  by  the  wind,  and 
why  those  with  slow  movement  often  escape  their  enemies.  On  the  other 
hand,  insects  may  be  readily  touched  or  caught  if  the  movements  are  suf- 
ficiently slow.  For  them  an  object  that  ceases  to  move  merges  at  once 
into  the  vague  background. 

Discrimination  of  form. — As  a  result  of  simple  experiments  with  a 
spider,  bee,  and  fly,  Dahl  (1889:243)  found  himself  in  agreement  with 
Lubbock  and  Forel  as  to  the  ability  of  insects  to  distinguish  forms,  and  in 
opposition  to  the  conclusions  of  Plateau.  He  regarded  the  statement  of 
the  latter  that  insects  often  deceive  themselves  by  flying  to  unopened 
flowers  as  indicating  that  they  are  attracted  primarily  by  color  rather 
than  form,  and  not  that  they  are  unable  to  distinguish  forms.  He  also 
observed  (Knuth,  1898:45)  that  in  spring  young  bees  light  on  flowers 
whose  nectar  is  too  deep-seated  for  them  and  make  vain  endeavors  to  reach 
it,  while  the  older  bees  merely  come  near  and  fly  away  without  landing. 
This  indicates  that  the  latter  recognize  the  flower  on  sight  as  one  with 
unavailable  honey,  since  guidance  by  odor  would  make  it  unnecessary 
for  them  to  approach  the  flower. 

Vision  in  honey-bees. — Buttel-Reepen  stated  that  bees  do  not  find 
their  way  home  when  thrown  up  into  the  air  at  dusk,  not  far  from  the 
hive;  they  make  several  small  circles  and  fall  to  the  ground  completely 
lost.  Their  flight  is  often  strongly  influenced  by  dark  clouds,  especially 
during  the  honey-flow,  when  the  approach  of  a  storm  sends  thousands 
of  bees  scurrying  back  to  the  hives.  In  their  haste  many  blunders  are 
made  in  entering,  which  would  not  be  true  if  they  were  drawn  to  the  proper 
hive  like  a  magnet  by  the  "unknown  force."  It  was  also  observed  that 
when  they  went  to  the  wrong  hive,  they  tried  to  enter  as  at  their  own, 
even  when  no  entrance  was  present,  showing  that  they  had  a  memory 
picture  of  their  hive,  though  they  had  mistaken  it.    He  also  cited  an  in- 


HOMING   FACULTY.  217 

6tance  of  bees  flying  against  a  gable  painted  sky-blue  that  they  had  regu- 
larly avoided  before,  and  one  of  young  bees  issuing  from  a  blue  hive  and 
flying  on  their  return  to  other  blue  ones  by  mistake,  but  never  to  those 
painted  in  other  colors. 

Vision  in  ants. — Fielde  (1902:599),  whose  studies  of  vision  in  ants 
were  in  agreement  with  those  of  Lubbock  and  Forel,  stated  that — 

"The  ants  manifested  no  liking  for  any  of  the  rays  of  light.  If  obliged  to  stay  in 
light  rays  of  some  sort,  the  rays  of  longer  wave-lengths  are  preferred  to  those  of  shorter 
wave-lengths.  Dividing  the  spectrum,  as  we  know  it,  into  red,  green,  and  violet, 
we  may  say  that  to  the  ants'  eyes  red  and  green  are  most  like  the  darkness  that  they 
prefer  and  that  violet  is  to  them  most  luminous;  or  that  the  red  and  green  are  less 
visible  to  them  than  is  violet.  In  this  regard  the  eyes  of  the  ant  appear  to  be  the  re- 
verse of  our  own.  Our  eyes  perceive  in  the  spectrum  three  fundamental  colors — red, 
green,  and  violet.  The  eyes  of  the  ant  perceive  there  only  two  fundamental  colors — 
one  made  up  of  the  red  and  green  rays,  the  other  of  the  violet  and  ultra-violet  rays. 

"It  appears  that  the  eye  of  the  ant  is  not  well  adapted  to  the  reception  of  light-rays 
whose  wave-length  is  longer  than  in  the  violet  rays ;  that  it  receives  blue  and  indigo 
more  perfectly  than  red,  orange,  yellow,  and  green;  and  that  there  is  a  sudden  in- 
crease of  luminosity  in  the  light  rays  at  that  point  in  the  spectrum  where  violet  be- 
gins for  our  eyes.  The  ants  may  discern  colors,  and  yet  have  no  preferences  among 
the  colors  discerned.  Color  is  determined  by  the  wave-length  in  the  light-ray,  and 
since  ants  discriminate  between  rays  of  different  wave-lengths,  they  probably  perceive 
color  in  the  rays.    Sensitivity  to  the  length  of  the  wave  indicates  perception  of  color." 

The  role  of  ultra-violet  in  attraction. — Richtmyer  (1922)  has  de- 
termined the  ultra-violet  reflection  of  a  number  of  Colorado  flowers  with 
reference  to  a  possible  influence  in  attraction.  He  considers  that  the  effect 
of  ultra-violet  in  attraction  involves  two  questions:  (1)  do  insects  "see" 
ultra-violet  in  the  sense  that  they  seem  to  "see"  the  rays  visible  to  us? 
(2)  is  the  ultra-violet  reflected  by  flowers  present  in  sufficient  degree  to 
play  an  important  part  in  rendering  flowers  visible  to  insects?  It  was 
found  that  few  of  the  flowers  reflected  any  considerable  proportion  of 
ultra-violet,  only  4  of  the  25  studied  reflecting  more  than  10  per  cent  of 
radiation  shorter  than  0.38  wi.  These  were  Laciniaria  punctata,  Oenothera 
biennis,  Rudbeckia  laciniata,  and  Solanum  rostratum.  Certain  yellow  flow- 
ers showed  a  distinct  ultra-violet  reflection  band,  particularly  well  marked 
in  Rudbeckia,  but  others  such  as  Solidago  and  Ratibida  gave  no  trace  of 
such  a  band.  The  flowers  differed  from  each  other  in  the  reflection  of  ultra- 
violet just  as  much  and  as  erratically  as  in  that  of  the  visible  spectrum. 
It  might  be  expected  that  a  white  flower,  which  reflects  the  visible  rays 
in  approximately  equal  proportions,  would  also  reflect  a  considerable 
amount  of  ultra-violet,  but  this  is  not  the  case.  They  gave  a  high  reflection 
of  light  longer  than  0.42  or  0.43  n,  but  none  of  them  reflected  more  than  4 
per  cent  of  0.39  /j..  The  most  striking  case  was  that  of  Argemone  platyceras, 
with  a  relative  coefficient  of  reflection  of  more  than  75  per  cent  at  0.41  n 
and  of  only  4  per  cent  at  0.39  ju. 

THE  HOMING  FACULTY  IN  BEES  AND  WASPS. 

Fabre's  experiments  with  bees  and  wasps. — In  his  "Souvenirs  Ento- 
mologiques"  (1879:299,  1882:99),  Fabre  recounted  his  studies  of  the  horn- 


218  PRINCIPLES   AND   CONCLUSIONS. 

ing  of  bees  belonging  to  two  species  of  Chalicodoma.  In  the  first  series 
the  insects  were  released  at  4  km.  from  their  nests;  of  the  first  2,  one  returned 
the  next  morning,  but  the  other  never  reappeared,  while  in  the  second  case, 
3  of  the  5  were  noted  the  following  morning.  In  the  third  experiment  40 
bees  were  freed,  but  only  half  of  these  flew  away  from  the  spot.  Once 
free,  the  bees  fled  as  though  frightened,  some  in  one  direction  and  some  in 
the  other.  The  first  2  returned  to  the  nests  in  three-quarters  of  an  hour 
and  3  others  toward  sundown,  while  10  more  were  observed  the  next  morn- 
ing, making  a  total  of  15  to  return  out  of  the  20  released.  All  told,  19  found 
their  way  home  out  of  27,  disregarding  those  thought  to  be  injured.  These 
were  supposed  to  have  found  their  way  back  in  spite  of  the  contrary  winds 
and  their  ignorance  of  the  places  to  which  they  were  carried.  It  is  obvious, 
however,  that  the  assumption  that  the  bees  had  never  wandered  so  far 
from  home  and  had  never  seen  these  places  was  a  gratuitous  one.  It 
afforded  exceedingly  tenuous  support  for  the  conclusion  that  they  were 
certainly  not  guided  by  memory  on  the  homeward  journey,  but  by  some 
special  faculty,  not  to  be  explained  but  recognizable  by  its  astonishing 
effects. 

In  the  second  series,  10  bees  of  the  same  genus  were  placed  in  a  bag  and 
carried  a  kilometer  distant,  where  the  bag  was  whirled  rapidly  about. 
They  were  then  taken  in  the  opposite  direction  to  a  distance  of  4  km. 
from  their  home  and  again  whirled  around  before  they  were  released  one 
at  a  time.  The  first  bee  traversed  the  distance  in  a  quarter  of  an  hour 
and  2  others  returned  several  hours  later,  but  the  remaining  7  did  not  re- 
appear. The  following  day  the  first  bee  reached  home  in  5  minutes  and  2 
more  in  about  an  hour,  while  the  other  7  failed  to  appear.  When  49  bees 
were  released,  the  majority  started  in  the  right  direction,  the  first  arriving 
in  15  minutes  and  11  within  an  hour  and  a  half;  6  more  appeared  within 
the  next  5  hours,  making  a  total  of  17  out  of  49,  while  in  the  next  test  7 
bees  out  of  20  found  the  way  back.  The  bees  in  the  next  experiment  were 
taken  over  2  miles  away,  2  returning  in  an  hour  and  a  half  and  7  more  in 
3  hours  and  a  half,  making  9  out  of  the  total  of  40.  Finally,  15  bees  were 
marked  with  rose  and  carried  by  a  roundabout  route  of  over  5  miles,  while 
a  second  15  were  marked  with  blue  and  taken  directly  to  the  spot,  a  distance 
of  a  mile  and  a  half.  All  were  released  at  noon,  and  by  5  o'clock  7  "rose" 
and  6  "blue"  bees  had  returned,  the  long  detour  making  no  appreciable 
difference.  Fabre  regarded  these  results  as  conclusive,  neither  the  whirling 
of  the  sack,  the  obstacles  of  hill  and  forest,  nor  the  devious  route  being 
able  to  hinder  Chalicodoma  from  returning  to  the  nest. 

Lubbock's  and  Ford's  critiques  of  Fabre's  conclusions. — Lubbock's 
discussion  of  Fabre's  results  is  so  detailed  and  conclusive  that  quotation 
alone  can  do  it  justice  (1888:264): 

"I  am  not  ashamed  to  confess  that,  charmed  with  M.  Fabre's  enthusiasm,  dazzled  by 
his  eloquence  and  ingenuity,  I  was  at  first  disposed  to  adopt  his  view.  Calmer  considera- 
tion, however,  led  me  to  doubt,  and  though  his  observations  are  most  ingenious  and  are 
very  amusingly  described,  they  do  not  carry  conviction  to  my  mind.  There  are  two 
points  especially  to  be  considered:  (1)  the  direction  taken  by  the  bees  when  released; 
(2)  the  success  of  the  bees  in  making  good  their  return  home. 

"As  regards  the  last  point,  it  will  be  observed  that  the  successful  bees  were  in  the  following 
proportion,  viz,  3  out  of  10,  4  of  10,  17  of  49,  7  of  20,  9  of  40,  7  of  15,  or  a  total  of  47  out 


HOMING   FACULTY.  219 

of  144.  This  is  not  a  very  large  proportion.  Out  of  the  whole  number  no  less  than  97 
appear  to  have  lost  their  way.  May  not  the  47  have  found  theirs  by  sight  or  by  accident? 
Instinct,  however  inferior  to  reason,  has  the  advantage  of  being  generally  unerring.  When 
2  out  of  3  bees  went  wrong,  we  may,  I  think,  safely  dismiss  the  idea  of  instinct.  Moreover, 
the  distance  from  home  was  only  \x/%  to  2  miles.  Now,  bees  certainly  know  the  country 
for  some  distance  around  their  home;  how  far  they  generally  forage  I  believe  we  have 
no  certain  information,  but  it  seems  not  unreasonable  to  suppose  that  if  they  once  came 
within  a  mile  of  their  nest  they  would  find  themselves  within  ken  of  some  familiar  landmark. 
Now,  if  we  suppose  that  150  bees  are  let  out  2  miles  from  home  and  that  they  flew  away 
at  random,  distributing  themselves  equally  in  all  directions,  a  little  consideration  will 
show  that  some  25  of  them  would  find  themselves  within  a  mile  of  home  and  consequently 
would  know  where  they  were.  I  have  never  myself  experimented  with  Chalicodomas, 
but  I  have  discovered  that  if  a  hive-bee  is  taken  to  a  distance,  she  behaves  as  a  pigeon 
does  under  similar  circumstances;  that  is  to  say,  she  flies  round  and  round,  gradually 
rising  higher  and  higher  and  enlarging  her  circle,  until  I  suppose  her  strength  fails  or  she 
comes  within  sight  of  some  known  object.  Again,  if  the  bees  had  returned  by  a  sense  of 
direction,  they  would  have  been  back  in  a  few  minutes.  To  fly  \Yi  or  2  miles  would  not 
take  5  minutes.  One  bee  out  of  the  147  did  it  in  that  time,  but  the  others  took  1,  2,  3,  or 
even  5  hours.  Surely,  then,  it  is  reasonable  to  suppose  that  these  lost  some  time  before 
they  came  in  sight  of  any  object  known  to  them. 

"Fabre  observes  that  the  great  majority  of  his  Chalicodomas  at  once  took  the  direction 
home.  He  confesses,  however,  that  it  is  not  always  easy  to  follow  bees  with  the  eye. 
Admitting  the  fact,  it  seems  to  me  far  from  impossible  that  the  bees  knew  where  they  were; 
and  at  any  rate,  this  does  not  seem  so  improbable  that  we  should  be  driven  to  admit  the 
existence  of  a  new  sense,  which  we  ought  to  assume  only  as  a  last  resource.  Moreover, 
Fabre  himself  says:  'When  the  rapidity  of  flight  permitted  me  to  note  the  direction  taken,' 
which  seems  to  imply  doubt.  Indeed,  some  years  previously  he  had  made  a  similar  experi- 
ment with  the  same  species,  but  taking  them  direct  to  the  point  rather  over  2  miles  from 
the  nest  and  not  whirling  them  round  his  head.  In  this  case  some  went  in  one  direction, 
some  in  another.  It  certainly  would  be  remarkable  if  bees  which  were  taken  direct  missed 
their  way,  while  those  which  were  whirled  round  and  round  went  straight  home.  Moreover, 
it  appears,  after  all,  as  a  matter  of  fact,  that  they  did  not  fly  straight  home.  If  they  had 
done  so,  they  would  have  been  back  in  3  or  4  minutes,  whereas  they  took  far  longer.  Even 
then,  if  they  started  in  the  right  direction,  it  is  clear  that  they  did  not  adhere  to  it. 

"Romanes's  experiments,  likewise,  as  he  himself  says,  entirely  confirm  the  opinion  I 
have  ventured  to  express,  that  there  is  no  sufficient  evidence  among  insects  of  anything 
which  can  justly  be  called  a  'sense  of  direction.'" 

Forel  (1900,  1908:72,  215)  also  emphasized  the  discrepancy  between 
Fabre's  results  and  his  conclusions. 

"Instead  of  attributing  these  facts  to  an  instinct  of  direction,  I  explain  them  as  follows: 
aerial  insects  and  aerial  beings  in  general,  soaring  above  terrestrial  objects  ought  to  have, — 
and  have,  a  knowledge  of  places  very  different  from  that  of  wingless  ones.  If  we  reflect 
on  the  geographical  coup  d'oeil  'as  the  crow  flies'  that  one  obtains  on  the  summit  of  a  hillock, 
we  shall  have  a  feeble  idea  of  what  the  vision  of  an  aerial  being  can  be,  with  this  difference, 
that  in  the  twinkling  of  an  eye  it  moves  and  alters  its  horizons,  which  we  can  not  do.  In 
20  minutes  the  Chalicodoma  of  Fabre  had  travelled  over  their  3  kilometers!  This  experi- 
ment simply  proves  to  me  the  very  instructive  and  interesting  fact  that  the  Chalicodoma 
knew  the  places  within  a  radius  of  a  league,  at  any  rate.  Those  which  did  not  find  their 
way  were  probably  newly  hatched  and  had  not  pushed  their  reconnaissances  so  far. 

"If  a  mysterious  sense  of  direction  had  guided  them,  all  that  started  would  have  returned. 
Weismann  thinks  rightly  that  the  bees,  set  free  in  this  unknown  and  to  them  distasteful 
place,  would  have  been  attracted  by  the  sight  of  the  hill.  Once  there,  the  oldest,  those  that 
knew  the  surroundings  best,  would  have  found  a  landmark  and  a  road.  Indeed  we  see 
even  pigeons  often  go  off  in  various  directions  at  first.  Is  it  not  significant  thus  to  see 
mason-bees,  placed  under  the  same  conditions,  conduct  themselves  in  miniature  like 
carrier-pigeons,  without  possessing  however  any  vestibular  or  otolithic  apparatus?  The 
circle  of  their  knowledge  of  places  does  not  appear  to  go  beyond  4  kilometers;  that  of 
highly  trained  pigeons  appears  to  reach  500.     There  is  no  striking  disproportion  therein. 


220  PRINCIPLES  AND   CONCLUSIONS. 

"I  hope  to  prove  that  any  mystic  or  mysterious  theory  of  special  sense,  sixth  sense, 
magnetism,  etc.,  is  as  superfluous  as  false  for  the  whole  animal  series.  The  known  senses, 
their  variations,  and  the  memories  which  are  derived  from  them  explain  everything" 
(p.  196). 

As  a  result  of  experiments  of  his  own  (1895;  cf.  Rau,  1918:278),  Weis- 
mann  concluded  also  that  "the  only  correct  solution  of  the  enigma  of 
path-finding  by  Chalicodoma  is  that  the  insects  find  their  way  back  with 
their  eyes."     (See  also  Perez,  1895.) 

Homing  faculty  of  bees. — Romanes  (1885:630)  conducted  observations 
to  determine  whether  honey-bees  find  their  way  home  by  means  of  land- 
marks or  by  means  of  a  mysterious  sense.  A  hive  of  bees  was  placed  in  a 
basement  room  of  a  house  situated  several  hundred  yards  from  the  coast, 
with  flower  gardens  on  each  side  and  lawns  between  the  house  and  the  sea. 
A  definite  number  of  bees  was  used  in  each  experiment  and  those  that 
returned  were  caught  by  means  of  birdlime.  The  first  score  of  individuals 
were  taken  out  to  sea,  whence  none  of  them  returned;  the  second  lot  was 
liberated  on  the  shore,  but  none  returned.  The  same  result  was  obtained 
when  the  next  lot  was  released  on  the  lawn  between  the  shore  and  the 
house,  although  the  distance  to  the  hive  was  not  over  200  yards.  Finally, 
when  bees  were  freed  in  different  parts  of  the  garden,  they  were  always 
found  stuck  in  the  birdlime  within  a  few  minutes,  often  arriving  before 
the  observer  could  reach  the  hive.  As  the  garden  was  a  large  one,  many 
of  these  bees  had  to  fly  a  longer  distance  than  those  released  on  the  lawn 
and  their  uniform  success  in  reaching  home  quickly  was  due  to  their  special 
knowledge  of  the  garden.  The  results  convinced  Romanes  that  bees  de- 
pend entirely  upon  their  special  knowledge  of  a  district  or  landmarks  and 
not  upon  any  general  sense  of  direction. 

Sense  of  direction  in  ground-wasps. — The  Peckhams  (1887:113) 
performed  a  number  of  experiments  to  determine  whether  wasps  possess 
a  mysterious  sense  that  enables  them  to  fly  in  a  straight  line  to  any  desired 
point,  even  though  they  have  never  been  over  the  fine  before.  When  63 
workers  were  carried  200  yards  west  to  the  top  of  a  hill  in  sight  of  the  nest 
and  10  released,  they  flew  off  in  all  directions,  not  taking  the  east  toward 
the  nest  oftener  than  the  other  directions.  Three,  after  circling  about, 
settled  again  on  the  stump,  but  after  some  hesitation  started  off.  When 
20  wasps,  10  of  which  were  marked,  were  set  free  on  a  lake,  nearly  all 
flew  in  the  direction  of  the  wind,  toward  the  nest,  but  in  the  next  test 
with  26  individuals,  6  took  a  direction  opposite  to  that  of  the  nest,  10 
returned  to  the  boat  and  seemed  loath  to  leave,  while  several  seemed  to 
change  their  minds  and  altered  their  courses.  Two  days  later  32  wasps 
were  released  on  the  lake  a  half-mile  north  of  the  nest;  8  of  these  returned 
to  the  boat,  some  of  them  twice,  6  or  7  flew  in  a  straight  fine  against  the 
wind  and  over  the  lake  to  the  nest,  while  17  or  18  flew  toward  the  shore. 
A  second  group  of  40  was  released,  to  fly  in  all  directions,  but  most  of  them 
returned  to  the  boat.  Of  the  135  wasps  set  free,  it  seemed  fairly  certain 
that  they  did  not  fly  toward  their  nest  as  frequently  as  in  an  opposite 
direction.  It  also  appeared  that  they  were  at  a  loss  to  know  which  way  to 
go,  since  they  often  returned  once  or  twice  for  a  new  start.  Of  55  wasps 
released  in  a  later  experiment,  39  returned  to  the  nest  in  about  an  hour's 
time.    When  38  workers  were  set  free  in  a  room  with  opposite  windows, 


HOMING   FACULTY.  221 

22  flew  through  the  window  away  from  the  nest,  16  through  the  one  toward 
it;  the  majority  returned  in  the  first  15  minutes,  but  they  continued  to 
arrive  for  another  quarter  of  an  hour. 

The  experiments  all  served  to  show  that  the  two  species  of  wasps  em- 
ployed have  no  sense  of  direction  in  the  form  of  a  mysterious  second  sense 
or  of  an  ability  to  keep  track  of  the  turns  and  changes  in  a  journey.  In 
spite  of  the  fact  that  the  wire  cage  permitted  the  use  of  sight,  they  fre- 
quently started  in  a  wrong  direction  as  they  flew  out.  In  many  instances, 
however,  these  wasps  returned  to  the  nest  and  it  seems  probable  that  they 
did  this  by  rising  higher  and  higher  in  the  air  and  discovering  some  objects 
that  served  them  as  landmarks. 

Disturbance  of  memory  in  wasps. — In  their  study  of  the  homing  in 
solitary  wasps  (1898:367),  the  Peckhams  concluded  that  if  these  had  an 
innate  sense  of  direction  they  would  not  need  to  make  a  study  of  the  sur- 
roundings of  the  nest  in  order  to  find  the  way  back,  but  in  the  absence  of 
such  a  sense  common  prudence  would  require  the  careful  inspection  of  the 
location  before  the  outward  flight.  After  days  spent  in  flying  about  the 
garden,  it  would  seem  that  further  study  of  the  precise  locality  might  be 
superfluous,  but  the  wasps  did  not  find  it  so.  They  made  repeated  and 
detailed  studies  of  the  surroundings  of  the  nests,  and  when  their  prey  was 
laid  down  for  a  moment  on  the  return,  they  noted  the  place  carefully  before 
leaving  it.  If  the  scrutiny  of  the  objects  about  the  nest  makes  no  impres- 
sion on  the  wasp,  she  should  not  be  bothered  or  misled  when  weeds  and 
stones  are  removed  and  the  ground  smoothed,  but  this  is  just  what  happens. 
Aporus  fasciatus  lost  her  way  entirely  when  a  leaf  that  covered  the  nest 
was  broken  off,  but  found  it  readily  when  this  was  replaced.  All  the  species 
of  Cerceris  were  extremely  annoyed  by  new  objects  placed  near  the  nests, 
and  Ammophila  refused  to  make  use  of  her  burrow  after  deep  lines  were 
drawn  in  the  dust  before  it.  The  same  annoyance  was  exhibited  when 
any  change  whatever  was  made  near  the  spot  where  the  prey  was  placed, 
and  experience  showed  how  important  it  was  not  to  disarrange  the  grass 
or  other  plants  on  such  occasions.  Marchal  (1900:1113)  has  given  an 
account  of  the  errors  made  by  Pompilus  in  the  return  to  the  nest  and  reaches 
a  similar  conclusion  to  the  effect  that  it  is  not  guided  by  a  special  sense 
of  direction,  but  solely  by  vision  and  memory. 

Observations  on  the  homing  of  Bembex  and  Pompilus. — Stimu- 
lated by  the  observations  of  Fabre  on  Bembex  (1879:261),  which  led  to  the 
conclusion  that  neither  memory  of  place,  sight,  nor  smell  guided  the  insect, 
Bouvier  (1900:874)  investigated  the  behavior  of  Bembex  labiatus.  His 
first  results  were  in  agreement  with  those  of  Fabre  to  the  effect  that  the 
wasp  always  returned  close  to  the  entrance  of  its  nest,  regardless  of  the 
substances  used  to  mask  this.  However,  when  the  objects  have  a  consider- 
able size,  the  insect  is  completely  lost  and  sometimes  spends  hours  seeking 
here  and  there  before  relocating  its  burrow.  When  the  latter  was  covered 
with  a  flat  stone  about  a  decimeter  in  size,  the  wasp  lighted  on  the  stone, 
scratched  it,  hunted  beneath  it,  and  found  the  entrance  only  after  much 
effort.  The  next  day  the  stone  was  displaced  about  2  dm.  from  the  new 
entrance  that  had  been  made,  with  the  result  that  the  insect  flew  at  once 
to  the  edge  of  the  stone  and  began  to  dig  as  though  at  the  right  place.  •  He 


222  PRINCIPLES  AND   CONCLUSIONS. 

was  twice  driven  away,  only  to  return  and  start  digging.  Finally,  the  rock 
was  restored  to  its  original  position,  and  the  wasp  found  the  entrance 
immediately.  Clearing  away  the  plants  and  smoothing  the  sand  about  a 
burrow  for  a  space  of  7  or  8  square  decimeters  sufficed  to  mislead  Bembex 
entirely,  and  it  was  only  after  a  long  time  spent  in  digging  here  and  there 
that  the  entrance  was  rediscovered.  Bouvier  concluded  that  memory  of 
place  and  vision  play  an  essential  if  not  exclusive  role  in  the  wonderful 
facility  with  which  Bembex  returns  to  the  entrance  to  its  nest.  Bouvier 
has  also  given  an  admirable  discussion  of  the  faculty  of  orientation  with 
insects  and  other  articulates  (1922:230,  251). 

Marchand  (1900:248)  found  that  when  a  plant  growing  about  5  cm. 
from  the  burrow  of  Bembex  was  displaced  about  the  same  distance,  the 
insect  was  unable  to  relocate  the  entrance  and  hunted  vainly  in  all  directions 
for  several  minutes.  The  plant  was  then  restored  to  the  original  position, 
and  upon  its  return  the  wasp  flew  close  to  it  and  soon  found  the  entrance 
to  his  nest. 

Memory  of  place  in  Osmia. — Ferton  (1905:89)  has  made  observations 
on  Osmia  rufohirta  which  indicate  that  this  solitary  bee  possesses  the  same 
remarkable  power  of  memory  for  place  as  the  social  bees  and  the  wasps. 
After  closing  its  nest  in  a  shell  of  Helix,  an  individual  of  this  species  moved 
it  to  a  new  position  a  dozen  centimeters  away  and  then  went  to  the  plant 
the  leaves  of  which  it  was  using  to  make  a  paste.  On  its  return  flights  it 
first  flew  to  position  A,  slackened  its  speed  without  alighting,  and  then  went 
directly  to  position  B,  a  path  that  it  followed  for  a  quarter  of  an  hour  or 
more.  The  observer  moved  the  shell  to  a  new  position  at  C,  where  the  bee 
found  it  after  some  trouble.  On  leaving,  the  latter  made  several  vertical 
flights  of  orientation  above  the  nest  before  returning  to  the  plant.  On 
coming  back  it  took  the  path  ABC,  though  when  it  went  to  another  plant 
growing  near  C,  it  returned  directly  to  the  latter.  Soon  afterward  it 
carried  the  shell  back  to  A  and  again  began  to  work  on  the  original  plant. 
On  its  return  it  passed  A  and,  making  a  slight  turn  toward  B,  reached  the 
point  C,  whence  it  returned  to  A,  after  determining  the  absence  of  the  nest 
at  C.  This  experiment,  with  others  that  were  repeated  several  times,  dem- 
onstrated that  this  species  is  guided  by  its  memory  of  place.  The  results 
obtained  with  Osmia  ferruginea  led  to  the  same  conclusion,  but  as  this  spe- 
cies does  not  have  the  habit  of  moving  its  shell,  it  is  less  skillful  in  relocating 
it  and  consequently  has  a  poorer  memory. 

The  manner  in  which  Osmia  searches  for  its  nest  when  displaced  indicates 
that  it  is  guided  chiefly  by  vision.  It  lands  upon  all  the  shells  found  in  its 
exploration,  which  would  not  be  the  case  if  it  were  guided  by  smell  alone. 
However,  the  bees  of  this  genus  also  employ  the  sense  of  smell,  especially 
that  of  contact.  Moreover,  they  can  make  use  of  this  sense  at  a  distance, 
as  when  it  is  used  to  guide  them  to  their  favorite  flowers.  It  is  unnecessary 
to  have  recourse  to  the  unlikely  hypothesis  of  an  unknown  sense,  since 
vision,  smell  at  a  distance  and  in  contact,  and  memory  suffice  to  explain 
all  the  observed  facts  (1906:29). 

Ferton  (1908:578)  has  also  discussed  Pieron's  contention  that  the  homing 
of  Osmia  is  due  to  muscular  memory  and  rejects  this  except  for  movements 
repeated  a  great  many  times. 


HOMING   FACULTY.  223 

The  field  and  nest  flights  of  the  bumble-hee.— Wagner  (1907:51) 
has  considered  the  sense  of  direction  of  Bombus  under  the  following  cap- 
tions: (1)  observations  on  the  return  to  the  nest  by  running;  (2)  observations 
on  the  field  and  the  nest  flight;  (3)  observations  in  cages;  (4)  homing  in 
nature.  When  the  wings  were  cut  off,  Bombus  was  unable  to  return  to  the 
nest,  showing  that  it  was  not  guided  by  a  mysterious  sense  of  direction. 
Each  flight  of  this  bee  consists  of  two  separate  acts,  the  field  flight  and  the 
return  to  the  nest.  These  are  impressed  upon  the  memory  and  retained  by 
it  in  a  different  manner,  though  this  holds  much  more  fully  for  the  nest 
flight.  The  bumble-bee  finds  its  way  on  the  nest  flight  through  the  careful 
inspection  of  a  few  objects  in  the  proximity  of  the  nest  or  with  the  aid  of 
the  main  points  in  memory.  This  inspection,  as  well  as  the  correlated 
impression  on  the  memory,  can  result  only  from  the  position  of  the  body 
as  taken  on  the  return  journey  to  the  nest.  The  inspection  of  objects, 
which  leaves  recollections  of  their  features,  demands  a  special  behavior, 
namely,  a  zig-zag  flight  near  the  object;  objects  not  observed  in  this  manner 
are  not  impressed  on  the  memory  of  the  bee.  Such  a  zig-zag  flight  continues 
only  so  long  as  the  bee  can  see  the  objects  about  the  nest,  which  is  within  a 
radius  of  a  meter  at  most.  Beyond  this  sphere  of  vision  lies  one  of  orien- 
tation, which  includes  neither  nest  nor  the  small  objects  about  it,  but  only 
such  large  ones  as  can  be  distinguished  vaguely  at  a  distance  greater  than 
10  meters.  Beyond  this  the  flight  back  and  forth  is  guided  by  the  sense  of 
direction.  Even  within  the  sphere  of  vision  the  sight  of  the  bumble-bee 
is  incomplete  in  so  far  as  it  distinguishes  only  a  few  guide-points,  which 
are  rather  impressions  of  positions  than  of  definite  objects.  As  a  conse- 
quence, only  a  decreasingly  small  portion  of  the  way  to  and  from  its  nest 
remains  fixed  in  its  memory,  and  hence  the  sense  of  direction  plays  an 
important  role  in  the  field  flight  and  the  return  to  the  nest. 

The  homing  of  the  mud-dauber  wasp. — In  studying  the  homing 
habits  of  the  mud-dauber  (1908:215),  Turner  noticed  that  the  wasp  never 
flew  directly  to  its  nest,  but  always  alighted  on  a  certain  crack.  It  ascended 
this  crack  to  the  height  of  the  nest  and  then  turned  and  walked  to  the 
latter,  its  behavior  suggesting  that  the  crack  served  as  a  landmark.  The 
method  of  experiment  and  the  nature  of  the  evidence  may  be  obtained  from 
the  account  of  the  first  experiment: 

"The  lower  shade  of  window  number  one  was  raised  halfway  and  the  top  shade  as  far 
as  it  would  go.  While  the  wasp  was  out  of  the  room  all  the  blinds  of  windows  number  two 
to  six  were  closed,  except  the  upper  shade  of  window  number  four,  which  was  raised  as  far 
as  possible. 

"The  wasp  on  entering  through  window  number  one  flew  obliquely  upwards  across  the 
beam  of  light  from  window  number  four  to  the  upper  third  of  upright  C.  (This  line  of 
flight  was  convex  towards  the  east.)  It  then  flew  vertically  upwards  almost  to  the  ceiling, 
then  leftward  about  a  foot  (this  is  a  little  more  than  the  distance  of  the  nest  from  upright 
B)  and  examined  carefully  the  moulding.  Not  finding  the  nest,  it  began  flying  first  to  the 
right  and  then  to  the  left  in  constantly  elongating  ellipses  with  very  short  minor  axes. 
All  this  time  it  was  carefully  examining  the  moulding.  Occasionally  the  mud-dauber 
would  fly  downward  into  the  beam  of  light  and  then  resume  its  search.  In  its  lateral 
flights  the  wasp  sometimes  flew  as  far  to  the  east  as  upright  D  and  to  the  west  almost  as 
far  as  upright  B.  At  the  end  of  three  minutes  it  had  not  found  the  nest,  although  under 
former  conditions  of  illumination  it  required  only  half  a  minute  to  fly  from  window  number 
one  to  the  nest. 


224  PRINCIPLES  AND   CONCLUSIONS. 

"While  the  wasp  was  still  searching  for  the  nest,  the  top  shade  of  window  number  four 
was  lowered  and  the  corresponding  shade  of  window  number  three  raised  as  far  as  possible. 
This  reproduced  the  conditions  under  which  the  wasp  had  originally  worked.  Almost 
immediately  the  wasp  found  the  nest! 

"From  these  experiments  it  is  evident  that  in  finding  its  way  back  to  its  nest,  the  mud- 
dauber  is  guided  neither  by  what  is  known  as  a  homing  instinct  nor  by  what  Pieron  has 
called  a  kinesthetic  reflex;  for  if  either  assumption  were  true,  a  manipulation  of  the  light 
should  not  have  altered  the  wasp's  behavior.  Evidently  light  plays  a  prominent  role  in 
the  homing  of  wasps,  yet  the  behavior  of  the  mud-dauber  is  not  a  phototropism,  for  in  no 
case  did  the  wasp  so  orient  itself  as  to  have  the  major  axis  of  its  body  parallel  to  the  rays 
of  light.  Neither  is  the  wasp's  behavior  merely  a  reflex  response  either  to  brightness  or 
to  the  direction  of  the  rays  of  light;  for  if  that  were  the  case,  in  experiment  six,  when  all 
the  shades  of  windows  number  two  to  four  were  lowered  except  the  top  shade  of  window 
number  two,  the  wasp  should  have  flown,  not  to  the  wall  to  the  west  of  window  number 
three,  but  to  window  number  two.  But  brightness  is  not  the  only  factor  which  influences 
the  movements  of  this  wasp;  else,  when  all  the  shades  of  windows  number  two  to  six 
were  lowered,  it  would  have  been  impossible  for  it  to  rediscover  the  nest.  This  series  of 
experiments  warrants  the  induction  that,  in  the  wasp's  memory,  the  nest  is  located  in  a 
certain  direction  and  at  about  a  definite  distance  from  a  bright  patch  which  is  situated 
at  a  known  elevation  in  a  peculiar  environment. 

"  The  above  statement  predicates  to  wasps  memory  and  an  awareness  of  space  relations. 
As  to  the  existence  of  memory,  these  experiments  furnish  unequivocal  evidence,  and  they 
warrant  the  conclusion  that  the  flying  mud-dauber,  like  the  creeping  ant,  is  guided  by 
certain  landmarks,  and  that  light  plays  a  prominent  role  in  furnishing  such  landmarks." 

Experiments  on  the  orientation  of  bees  in  homing. — Frisch  (1914: 86) 
has  summarized  the  results  of  others  as  to  the  practical  value  of  painting 
hives  in  color  and  has  contributed  the  details  of  some  of  his  own  experiments 
in  this  field.  All  of  these  support  the  conclusion  that  honey-bees,  when 
their  hive  is  set  apart  from  the  neighboring  ones  by  means  of  color  in  a 
striking  manner,  utilize  this  as  the  chief  means  of  orientation  in  finding 
their  home.  They  further  show  that  bees  observe  not  only  the  color  of 
their  own  hive,  but  also  the  color  and  relative  position  of  neighboring  ones. 
In  consequence  the  bee-keeper  can  hardly  devise  a  better  and  more  certain 
way  of  enabling  bees  to  locate  their  own  hive  than  that  of  painting  it  in 
colors.  For  this,  however,  it  is  desirable  to  paint  the  entire  outside  and 
not  merely  the  landing-board  or  the  entrance.  Care  should  be  taken  not 
to  employ  for  neighboring  hives  colors  that  are  distinct  for  our  eyes  but  not 
for  those  of  the  bee,  such  as  blue  and  purple,  or  black  and  scarlet-red.  As 
a  result,  when  hives  are  numerous,  it  is  better  to  use  color  combinations  for 
each,  such  as  one-half  red  and  the  other  yellow,  rather  than  too  many 
colors  or  shades  which  may  merely  be  distinct  to  us. 

Homing  ability  in  Polistes. — The  Raus  (1918:273)  have  made  a 
number  of  experiments  on  the  homing  ability  of  the  wasp,  Polistes  pallipes, 
which  they  summarize  as  follows: 

"Out  of  33  queens  which  were  taken  for  various  distances  from  one-eighth  mile 
to  2.7  miles,  24  returned  to  the  nest.  Of  the  22  taken  out  for  the  first  time,  17  reached 
home;  of  the  11  which  had  made  previous  test  flights,  7  successfully  returned.  With 
the  workers,  the  results  were  quite  different.  Of  112  workers  that  were  used,  only 
28  returned,  and  those  that  returned  did  so  only  in  the  short  flights.  The  long  dis- 
tance tests  always  gave  negative  results.  Out  of  the  17  new  workers  that  were  ex- 
perimented upon,  none  returned;  of  the  33  old  workers,  14  came  back;  of  the  62 
workers  of  unknown  age,  14  returned.  According  to  the  law  of  chance,  it  is  easily 
possible  that  these  14  out  of  the  62  workers  of  unknown  age  may  have  been  old  ones. 


SMELL.  225 

Previous  experience  is  not  necessary  to  successful  flights;  27  successful  returns  out 
of  96  were  made  by  wasps  used  for  the  first  time,  but  only  1  out  of  16  wasps  that  had 
previous  flights  made  a  successful  second  trip.  Not  one  of  the  17  males  returned 
to  their  former  nests,  even  though  the  distance  for  16  of  them  was  only  one-eighth  mile. 
The  function  of  the  antenna?  is  not  the  sole  factor  in  bringing  them  home,  for  out  of 
24  mutilated  wasps,  18  successfully  returned.  Thus,  by  the  elimination  of  other 
faculties,  the  evidence  grows  stronger  that  vision  is  the  sense  whereby  the  insects 
regain  their  homes." 

SMELL. 

Sense  of  smell  in  insects  deprived  of  antennae. — Forel  (1886:184)  in- 
sisted that  the  experiments  of  Graber  (1885)  with  strong  odors  merely 
proved  whether  these  were  irritating  or  not  to  the  insects  concerned  and  that 
evidence  of  smell  could  be  obtained  only  by  causing  the  insect  to  recog- 
nize a  certain  substance  and  especially  to  distinguish  it  from  others  in 
a  constant  and  indubitable  manner.  As  an  example,  he  cited  the  case  of  a 
swarm  of  males  of  Saturnia  carpini  that  besieged  the  window  of  his  room 
after  some  females  had  hatched  out,  which  he  regarded,  together  with  many 
previous  observations  of  others,  as  demonstrating  in  insects  a  special 
sense  that  corresponds  to  that  in  man.  Further  demonstration  may  be 
furnished  by  the  removal  of  the  antennae  whenever  the  loss  of  these  or- 
gans carries  with  it  the  loss  of  the  sense  of  smell,  as  proved  to  be  the  case 
in  many  of  the  experiments  he  carried  out. 

When  the  antennae  were  removed  from  individuals  of  four  different 
genera  of  ants,  they  mingled  readily  without  harming  each  other,  and  they 
recognized  honey  only  when  the  mouth  touched  it  by  chance.  If  the  an- 
tennas were  removed  in  Formica  fusca  and  the  ants  placed  in  a  globe  with 
their  larvae,  cocoons,  and  soil,  they  did  not  attempt  the  slightest  digging 
or  give  the  larvae  the  least  care.  When  ants  of  another  species  were  added, 
they  did  them  no  harm,  but  when  the  anterior  tarsi  were  cut  off  above 
the  spine  in  the  same  species,  they  immediately  killed  other  ants  given 
them,  and  made  futile  efforts  to  dig  and  to  care  for  the  larvae.  A  repetition 
of  these  experiments  eight  years  later  gave  similar  results,  except  in  the 
case  of  Myrmica  ruginodis,  which  killed  other  ants  as  well  as  its  own  kind. 
In  the  case  of  Sarcophaga  vivipara  with  both  eyes  excised,  the  female  readily 
found  a  dead  mole  on  which  it  fed,  but  after  the  antennae  were  removed, 
it  paid  no  more  attention  to  the  mole,  even  when  placed  beside  it.  A  blue 
fly  which  also  fed  upon  the  mole  and  deposited  eggs  in  it  paid  no  attention 
whatever  to  it  after  the  antennae  had  been  removed,  in  spite  of  the  use  of 
its  eyes.  Two  other  individuals  of  Sarcophaga  behaved  in  similar  manner, 
while  a  very  active  Lucilia  caesar,  though  placed  on  the  mole,  ceased  eating 
and  depositing  eggs  as  soon  as  the  antennae  were  gone.  In  like  manner, 
beetles  of  several  genera  were  unable  to  rediscover  putrid  objects  after  the 
removal  of  the  antennae.  Males  of  Bombyx  mori,  which  perceived  the  fe- 
males at  a  distance  and  ran  to  them  directly,  were  no  longer  able  to  deter- 
mine the  direction  of  the  female  after  the  antennae  had  been  removed. 

In  an  experiment  with  a  wasp,  Polistes  gallicus,  three  individuals  were 
employed,  one  having  the  antennae  removed,  the  second  the  front  of  the 
head  with  the  sense-organs  of  the  mouth,  and  the  third  was  left  intact. 
In  repose  the  latter  was  able  to  recognize  honey  at  a  distance  of  a  centi- 


226  PRINCIPLES  AND  CONCLUSIONS. 

meter  and  followed  it  as  the  pin  covered  with  it  was  withdrawn.  The  second 
wasp  behaved  in  identical  fashion,  though  it  was  unable  to  sip  the  honey, 
while  the  first  was  absolutely  unable  to  perceive  the  honey  until  the  latter 
was  put  in  contact  with  its  mouth  or  to  follow  as  it  was  moved  away. 
To  determine  how  acute  the  sense  of  smell  is  in  bees,  Forel  placed  some 
hungry  honey-bees  in  a  glass  box  with  a  drop  of  honey  covered  with  a  disk 
of  wire  screen  with  large  meshes,  through  which  the  honey  could  be  read- 
ily reached.  In  spite  of  this  they  walked  back  and  forth  over  the  screen, 
passing  a  hundred  times  within  2  or  3  mm.  of  the  honey,  without  stopping 
or  suspecting  the  presence  of  the  food  they  sought.  As  soon  as  the  screen 
was  removed,  they  found  the  honey  by  chance  and  sipped  it  with  avidity. 
In  agreement  with  Lubbock,  it  was  concluded  that  honey-bees  guide 
themselves  almost  exclusively  by  sight,  their  antenna?  being  very  short, 
without  clubs,  and  having  olfactory  terminations  only  on  the  internal 
dorsal  face. 
The  following  conclusions  were  deduced  with  reference  to  smell : 

1.  With  many  insects  that  guide  themselves  primarily  by  vision,  as  with  dragon- 

flies  and  cicadas,  the  antennae  are  rudimentary  and  the  sense  of  smell  likewise. 
At  night  such  insects  are  immobile  and  by  day  all  their  acts  are  guided  by  sight 
(the  cicadas  also  perhaps  by  hearing). 

2.  The  sense  of  smell,  notwithstanding  the  objections  and  the  experiments  of  Graber, 

resides  in  the  antennae,  especially  in  the  swollen  or  perfoliate  part  in  which 
the  antennal  nerve  ramifies. 

3.  With  certain  insects,  especially  the  majority  of  the  Diptera,  the  antennae  are 

stiff  and  probably  serve  solely  or  almost  so  as  an  organ  of  smell. 

4.  But  with  other  insects  they  are  mobile  and  serve  at  the  same  time  to  smell  at  a 

distance  and  to  feel  near  at  hand.  This  is  true  of  Hymenoptera  in  the  highest 
degree. 

ForePs  criticisms  of  Graber's  results. — Emphasis  was  placed  by 
Forel  upon  the  fact  that  we  regard  as  odorous  substances  those  that  are 
odorous  for  us,  in  spite  of  the  fact  that  the  study  of  animals  shows  enor- 
mous differences  between  them  in  this  respect,  a  substance  extremely  odor- 
ous for  one  species  being  little  or  not  at  all  for  another.  This  general 
fact  was  recognized  by  Graber,  but  his  simple  and  uniform  method  of 
experimentation  failed  to  take  account  of  it.  Graber  placed  different 
insects  in  the  middle  of  a  box  divided  into  two  compartments  open  below. 
He  put  an  odorous  substance  in  the  top  of  one  of  them  and  observed  at 
the  end  of  a  certain  time  the  number  of  insects  in  each  part.  He  employed 
especially  substances  with  strong  and  often  corrosive  emanations,  and  in 
many  cases  found  that  insects  deprived  of  their  antennae  behaved  like 
normal  ones.  But  this  was  not  always  the  case,  Asphodius,  for  example, 
ceasing  to  gather  under  cow-dung  when  the  antennae  were  removed. 
This  was  because  Graber  had  made  the  proper  choice,  that  of  an  substance 
sought  by  this  insect  in  nature.  Moreover,  he  finally  stated  that  a  certain 
degree  of  smell  resided  in  the  antennae. 

In  the  case  of  Lucilia  caesar,  Graber  found  that  169  normal  flies  col- 
lected under  putrid  meat,  while  92  were  found  on  the  other  side,  but  with 
the  antennae  cut  off  the  respective  figures  were  101  and  39,  which  he 
thought  proved  irrefutably  that  they  had  smelled  the  meat  without  the  aid 


SMELL.  227 

of  antennae.  Forel  pointed  out  that  the  numbers  were  not  sufficiently 
different  to  prove  much,  and  this  is  confirmed  by  the  fact  that  the  respective 
percentages  for  meat  were  64  and  72.  In  addition,  the  odor  of  putrid 
meat  in  a  box  was  regarded  as  sufficiently  strong  to  provoke  tactile  or 
gustatory  reactions  quite  apart  from  smell,  while  flies  inclosed  in  a  box 
are  far  from  normal  in  their  response.  With  Formica  rufa,  Graber  found 
that  essence  of  rose  was  not  liked,  515  ants  collecting  in  the  empty  division, 
and  but  42  in  that  containing  the  essence,  while  with  the  antennas  cut  off 
the  respective  numbers  were  299  and  165,  figures  which  Forel  regarded 
as  insufficient  to  prove  that  ants  have  other  organs  of  smell  than  antennas. 
However  this  may  be,  he  declared  that  Graber  had  absolutely  not  proved 
that  ants  with  or  without  antennas  were  in  a  state  to  recognize  the  essence 
of  rose  as  such,  to  distinguish  it  from  another  substance,  or  to  find  it  when 
hidden.  Finally,  in  another  place  Graber  seemed  to  be  of  the  opinion 
that  these  responses  were  rather  of  the  nature  of  reaction  to  irritation 
than  smell.  In  the  case  of  Silpha  thoracica,  while  essence  of  rosemary 
quickly  produced  a  reaction  in  the  absence  of  antennas,  asafetida  did  not, 
but  with  the  antennas  present  the  response  to  both  was  equally  prompt. 

In  summarizing,  Forel  declared  that  the  experiments  of  Graber  ex- 
hibited a  very  superficial  knowledge  of  the  habits  of  insects,  often  lacked 
controls,  and  were  too  little  varied,  and  that  the  means  and  the  reagents 
employed  were  frequently  too  strong  and  took  no  account  of  the  habits 
or  needs  of  each  species.  Moreover,  after  seeking  the  location  of  the  sense 
of  smell  in  various  places  in  contradictory  fashion,  Graber  finally  stated 
that  "there  are  insects  in  which  the  antennas  play  a  preponderant  rdle 
in  the  distinction  of  weaker  odors,  food,  etc." 

In  a  later  paper  (1887:13)  Graber  himself  stated  that  the  stronger 
odors  usually  repel  insects  and  that  this  response  is  not  due  to  the  sense 
of  smell,  but  to  a  generally  very  painful  excitation  of  the  sense  of  feel, 
which  is  often  extraordinarily  developed.  As  a  consequence  of  a  number 
of  carefully  controlled  experiments,  he  reached  the  conclusion  that  Plat- 
eau's results  with  the  cockroach  (1876)  were  untrustworthy,  though  he  was 
able  to  confirm  the  statement  that  the  sense  of  smell  is  located  in  the 
antennas. 

Hauser's  experiments. — Hauser  (1880:367)  determined  the  effect  of 
removing  the  antennas  in  a  wide  range  of  insects  from  beetles  to  bees. 
The  loss  of  the  antennas  caused  many  individuals  to  become  sick  and  die, 
though  some  lived  for  weeks  afterward.  Coating  the  antennas  with  paraf- 
fin gave  the  same  results  as  extirpation.  Beetles  made  no  response  to 
a  clean  glass-rod,  but  when  this  was  dipped  in  carbolic  acid,  the  effect 
was  noticed  at  4  inches  and  the  insect  moved  away  quickly  as  the  rod 
was  brought  nearer.  It  reacted  even  more  strongly  to  turpentine  and 
acetic  acid.  The  experiments  were  repeated  on  the  second  day  after  the 
removal  of  the  antennas,  but  no  response  occurred.  This  was  in  spite  of 
the  fact  that  the  beetles  ate  more  heartily  after  the  operation  and  some 
lived  more  than  two  months.  Species  of  various  genera  gave  similar  re- 
sults, but  a  few  continued  to  respond  slightly.  Beetles  of  the  genus  Silpha 
lost  the  power  of  finding  putrid  meat  after  the  amputation  of  the  antennas, 
and  the  same  result  was  obtained  with  different  species  of  flies.  Male  and 


228  PRINCIPLES   AND   CONCLUSIONS. 

female  beetles  or  butterflies  that  mated  freely  when  normal  did  so  only 
occasionally  after  the  antennae  were  lost. 

Olfactory  pores. — Hicks  (1857-1860)  was  the  first  to  discover  the  pores 
now  termed  olfactory  by  Mclndoo,  who  summarizes  the  former's  results 
as  follows  (19142:38). 

"To  summarize  Hicks's  three  papers,  he  discovered  these  pores  on  the  halteres  and 
on  the  bases  of  the  wings  of  all  Diptera  examined;  on  the  bases  of  all  four  wings 
of  the  four- winged  tribes;  on  the  trochanter  and  femur  of  all  insects,  and  occasionally 
on  the  tibia.  He  examined  many  species  representing  various  insect  orders  and  found 
the  pores  even  on  the  lower  insects,  such  as  the  earwig.  In  such  wingless  insects  as 
the  worker  and  soldier  ants,  he  infers  that  these  pores  are  much  more  abundant  on 
the  legs  than  they  are  on  these  appendages  in  the  winged  insects.  Hicks  suggested 
an  olfactory  function  for  all  of  these  pores,  whether  on  the  wings  or  legs,  but  he  per- 
formed no  experiments  of  any  kind.  In  regard  to  smell  in  insects  and  the  function 
of  the  pores  on  the  legs,  he  says:  'The  delicacy  with  which  odors  are  perceived  by 
many  insects  argues  an  olfactory  apparatus  of  considerable  perfection;  and  it  seems 
to  me  not  impossible  that  these  latter-named  organs  (those  on  the  legs)  may  be  in 
some  way  connected  with  the  sense  of  smell,  or  perhaps  with  some  sense  not  to  be 
found  in  the  Vertebrata.'" 

Mclndoo  mentions  the  work  of  about  a  dozen  other  investigators  on 
these  pores,  two  of  whom  regarded  them  as  olfactory  in  function. 

Mclndoo's  own  studies  (1914)  of  the  pores  are  much  the  most  detailed 
and  comprehensive,  and  his  experiments  upon  their  function  appear  to 
be  the  most  extensive  in  the  entire  field  of  olfaction.  The  Hicks  vesicles 
or  olfactory  pores  consist  of  inverted  flasks  in  the  chitin  and  of  fusiform 
sense-cells  lying  beneath  the  mouths  of  the  flasks.  The  sense  fiber  pierces 
the  bottom  of  the  cone  and  enters  the  pore  aperture,  thus  coming  in  direct 
contact  with  the  air  containing  odorous  particles,  contrary  to  the  condition 
in  the  antennae,  where  the  odors  must  pass  through  a  hard  membrane 
in  order  to  stimulate  the  sense-cells.  In  the  case  of  the  honey-bee  the  pores 
are  found  on  the  bases  of  the  wings,  on  the  legs,  and  on  the  sting  of  worker 
and  queen.  They  also  occur  on  the  mouth-parts  of  all  Hymenoptera,  while 
they  are  lacking  on  the  antennae  of  the  honey-bee  and  probably  all  other 
Hymenoptera.  For  the  legs  of  ants  the  number  varies  from  211  to  356 
and  for  the  winged  ants  the  total  number  varies  from  463  to  1,090.  In  the 
honey-bee  the  queen  has  an  average  of  1,860,  the  worker  2,268,  and  the 
drone  2,604;  the  averages  for  all  four  wings  are  1,310,  1,510,  and  1,998, 
and  for  all  six  legs,  450,  658,  and  606  respectively,  the  sting  having  an  average 
of  100.  The  total  number  for  a  bumble-bee  was  1,627  and  for  a  wasp  1,957; 
the  number  of  isolated  pores  is  approximately  one-half  the  number  in  groups, 
except  in  the  worker  honey-bee,  where  it  is  somewhat  less. 

Experiments    with    antennae    removed,    mutilated,    or    coated. — 

Mclndoo  (1914  :  291)  finds  that  worker  bees  with  the  left  antennae 
pulled  off  at  the  base  reacted  to  the  three  essential  oils,  peppermint,  thyme, 
and  wintergreen,  in  an  average  of  4.6  seconds  in  contrast  to  2.3  seconds  for 
intact  individuals.  When  2  to  8  joints  of  the  other  antennae  were  removed, 
the  reaction-time  rose  proportionately  from  15  seconds  for  the  first  case  and 
88  for  the  last.  Bees  with  both  antennae  pulled  off  or  covered  with  celloidin 
failed  entirely  to  respond  to  these  oils.    Drones  with  4  or  5  joints  of  one 


SMELL.  229 

flagellum  missing  responded  to  6  of  the  10  odors  used  in  an  average  re- 
action-time of  3.16  seconds  in  contrast  to  2.9  seconds  for  unmutilated  ones. 
When  both  antennae  were  removed  from  workers,  none  responded  to  oil 
of  peppermint  held  within  a  half  inch  or  to  smoke,  while  all  the  normal 
bees  reacted  quickly  and  markedly.  Similar  experiments  with  other  oils 
yielded  no  reaction  in  the  case  of  50  mutilated  bees,  though  the  normal  ones 
never  failed  to  react. 

In  the  case  of  immature  bees  the  results  were  quite  different.  When 
both  the  antennae  of  workers  were  burned  off,  they  responded  readily  to 
the  three  essential  oils  by  moving  slightly  and  vibrating  the  stubs  of  the 
antennae.  Frequently,  however,  they  did  not  react  to  odors  or  anything 
else.  When  the  antennae  were  covered  with  glue  and  the  tarsi  of  the  front 
legs  burned  off  to  prevent  the  removal  of  the  glue,  most  of  the  bees  died 
in  a  few  days,  but  a  score  were  fairly  normal  and  responded  to  the  oils 
without  failure. 

Experiments  with  wings,  legs,  and  stings  mutilated. — 

"To  determine  the  function  of  these  pores,  the  wings,  legs,  and  stings  of  many  worker 
bees  were  mutilated  (Mclndoo,  19143:47).  The  behavior  of  the  mutilated  bees  was 
carefully  studied,  and  they  were  tested  with  odors  in  the  same  manner  as  were  the 
unmutilated  ones.  The  stings  of  100  workers  were  pulled  out.  These  bees  lived  30 
hours  on  an  average.  Twenty  of  them  were  tested  with  odors.  They  responded  only 
slightly  more  slowly  than  unmutilated  bees.  The  wings  of  28  workers  were  pulled 
off.  When  tested  with  odors,  these  bees  responded  one-eighth  as  rapidly  as  normal 
bees.  The  bases  of  the  wings  of  20  workers  were  covered  with  liquid  glue.  When 
tested,  these  bees  also  responded  one-eighth  as  rapidly  ao  unmutilated  ones.  The 
pores  on  the  legs  of  20  workers  were  covered  with  a  mixture  of  beeswax  and  vaseline. 
When  tested,  these  bees  responded  two-fifths  as  rapidly  as  unmutilated  workers. 
The  wings  were  pulled  off  and  the  pores  on  the  legs  of  20  workers  were  covered  with 
the  beeswax-vaseline  mixture.  When  tested  with  odors,  these  responded  one-twelfth 
as  rapidly  as  unmutilated  ones.  All  of  the  workers  with  mutilated  wings  and  legs 
lived  just  as  long  in  the  observation  cages  as  did  unmutilated  workers,  and  they  were 
absolutely  normal  in  all  respects,  except  that  they  reacted  to  odors  more  slowly." 

With  the  oils  and  other  odors  four  dealated  females  of  Formica  gave 
a  reaction-time  of  2.89  seconds  in  contrast  to  2.45  seconds  for  winged 
females  of  the  same  species.  Pulling  off  the  wings  of  7  males  removed 
92  per  cent  of  the  pores  and  increased  the  reaction-time  from  2.63  to  3.6 
seconds.  When  the  wing  bases  of  female  ants  were  covered  with  liquid 
glue  and  the  legs  with  beeswax-vaseline  mixture,  the  reaction-time  was 
about  doubled,  and  similar  results  were  obtained  with  Camponotus.  When 
males  of  the  latter  had  the  wings  pulled  off,  leaving  but  12  per  cent  of  the 
pores,  they  gave  a  reaction-time  of  3.49  seconds,  which  is  one  and  a  fourth 
times  that  of  the  normal  insects.  Worker  hornets  similarly  treated  gave 
nearly  thrice  the  reaction-time  for  normal  ones. 

Mclndoo's  criticisms  of  experiments  with  deantennate  insects. — 

"The  following  criticisms  concerning  the  physiological  experiments  performed 
with  the  antennae  of  the  various  insects  may  be  offered  (1914:342,  19143:54). 
Most  of  the  previous  investigators  have  studied  the  behavior  of  the  insects  investigated 
in  captivity  for  only  a  short  time,  while  the  remainder  have  paid  no  attention  at  all 
to  the  behavior  of  their  unmutilated  insects.    They  cut  off  either  a  few  joints  of  both 


230  PRINCIPLES   AND   CONCLUSIONS. 

antennae,  or  these  entire  appendages,  or  varnished  them  with  paraffin,  rubber,  and 
so  forth.  When  a  few  joints  are  severed,  the  sense  of  smell  is  apparently  weakened. 
This  is  true  for  bees  also.  When  both  antennae  are  amputated  or  varnished,  the  in- 
sects as  a  rule  fail  to  respond  to  substances  which  normally  affect  the  olfactory  sense. 
They  generally  fail  to  respond  to  odors  held  near  them  and  fail  to  find  food  in  cap- 
tivity, and  do  not  return  to  putrid  meat  and  dead  bodies  when  removed  from  such 
food.  Males  so  mutilated  as  a  rule  do  not  seek  females  and  show  no  responses  when 
females  are  placed  near  them.  Such  experiments  were  seriously  criticised  until  Hauser 
in  1880  presented  his  apparently  conclusive  results.  Many  of  the  insects  on  which  he 
experimented  with  the  antennae  amputated  became  sick  and  soon  died.  Most  of 
them  failed  to  respond  when  the  antennae  were  mutilated,  although  Carabus,  Melo- 
lontha,  and  Silpha  responded  slightly,  while  all  the  Hemiptera  that  he  used  responded 
almost  as  well  with  their  antennae  off  as  they  did  with  them  intact.  Only  40  per 
cent  of  the  ants  from  which  Miss  Fielde  cut  the  antennae  recovered  from  the  effect 
of  the  shock.  Not  one  of  these  observers  has  studied  the  behavior  of  the  species 
under  observation  sufficiently  to  know  exactly  how  long  they  live  in  captivity  with 
their  antennae  either  intact  or  mutilated.  No  one,  except  Miss  Fielde,  has  kept  a 
record  of  the  death  of  the  mutilated  and  normal  insects  so  accurate  that  one  might 
know  what  percentage  died  from  the  operation.  To  cut  off  some  other  appendage 
or  even  the  lower  part  of  the  head,  as  Forel  did,  is  not  a  fair  test,  because  such  oper- 
ations seldom  expose  sense-cells  and  never  any  nerve  equal  in  size  to  that  of  the  an- 
tennae, unless  one  pulls  off  the  wings.  When  the  wings  are  pulled  off,  the  large  nerve 
is  severed  between  the  masses  of  sense-cells  and  the  thorax,  and  the  sense-cells  are 
not  exposed  to  the  air,  as  they  are  when  antennae  are  removed.  Even  if  the  an- 
tennae are  cut  through  the  scape,  the  large  masses  of  sense  cells  belonging  to  John- 
ston's organs  are  severed.  When  the  lower  part  of  the  head  or  the  tarsi  are  cut  off, 
as  Forel  did,  no  nerves  are  exposed  to  the  air  except  ends  of  small  nerves.  From  the 
foregoing  it  is  only  reasonable  to  assume  that  when  the  antennae  of  any  insect  are 
injured  in  the  least  degree,  the  insect  is  no  longer  normal  and  if  it  fails  to  respond 
to  odors  placed  near  it,  this  negative  response  may  be  due  to  the  shock  of  the  injury." 

Present  status  as  to  the  seat  of  the  olfactory  sense. — In  spite  of 
the  obvious  merits  of  Mclndoo's  studies,  it  is  evident  that  further  in- 
vestigations will  be  necessary  to  decide  the  respective  claims  of  the  an- 
tennae and  the  olfactory  pores  as  the  organs  of  smell.  The  results  of  more 
than  a  score  of  investigators,  some  of  them,  such  as  Forel,  Graber,  Hauser, 
and  Plateau,  of  the  first  rank,  are  in  accord  as  to  the  olfactory  function 
of  the  antennae,  and  it  is  certain  that  their  conclusions  can  not  be  rejected 
without  a  repetition  of  their  most  decisive  experiments.  On  the  other  hand, 
many  of  Mclndoo's  are  similarly  decisive,  and  at  present  it  seems  quite 
possible  that  both  antennae  and  pores  have  to  do  with  smell.  The  burden 
of  proof  rests  upon  the  latter,  however,  since  they  lack  the  confirmation 
given  by  successive  investigators  to  the  function  of  the  antennae.  Mcln- 
doo  has  given  a  practically  complete  list  of  those  who  have  based  their 
conclusion  as  to  the  olfactory  function  of  the  antennae  upon  experi- 
mental evidence  (19143:14).  They  are  Dug6s  (1838),  Lefebvre  (1838), 
Ktister  (1844),  Perris  (1850),  Cornalia  (1856),  Donhoff  (1861),  Balbiani 
(1866),  Forel  (1874,  1878,  1886,  1901),  Trouvelot  (1877),  Layard  (1878), 
Slater  (1878),  Chatin  (1880),  Hauser  (1880),  Porter  (1883),  Graber  (1885, 
1887),  Plateau  (1886,  1902),  Dubois  (1895),  Mayor  (1900),  Gorka  (1900), 
Fielde  (1901,  1903),  Barrows  (1907),  and  Kellogg  (1907).  The  most  ex- 
tensive and  significant  studies  have  been  those  of  Forel,  Hauser,  Graber, 


SMELL.  231 

Plateau,  and  Mayor,  since  the  extirpation  of  the  antennae  in  most  cases  de- 
stroyed the  sense  of  smell  without  rendering  the  insects  otherwise  abnormal. 
Graber's  second  series  of  experiments  is  especially  important,  since  they 
led  him  to  abandon  his  former  view  that  the  antennae  were  not  olfactory 
organs.     (See  also  Schenk,  1903  :  573.) 

A  scrutiny  of  Mclndoo's  conclusions  shows  that  they  are  not  in  entire 
accord,  though  this  may  be  due  to  a  desire  to  avoid  overstatement.  The 
statements  concerned  are  as  follows: 

"These  results  indicate  that  the  olfactory  organs  are  located  elsewhere.  At  most 
it  can  be  claimed  only  that  the  antennae  may  assist  in  the  receiving  of  odor  stimuli" 
(1914:  297).  "It  may  now  be  assumed  that  these  pores  constitute  the  olfactory  organs 
in  the  honey-bee,  and  perhaps  in  insects  in  general"  (lb.,  341).  "Then  it  will  be  real- 
ized that  the  antennas  can  no  longer  be  regarded  as  the  seat  of  the  sense  of  smell 
in  insects"  (lb.  345).  "In  conclusion,  it  seems  that  the  organs  called  olfactory  pores 
by  the  author  are  the  true  olfactory  apparatus  in  Hymenoptera  and  possibly  in  all 
insects  and  that  the  antennae   play  no  part  in  receiving  odor  stimuli"  (19143:56). 

The  mature  bees  used  in  experiments  with  the  antennae  cut  off  gave  either 
greatly  delayed  reactions  or  none  at  all,  but  when  these  were  burned  off, 
the  reaction-time  was  but  slightly  increased.  However,  the  latter  lived 
an  average  of  5%  days,  while  the  former  in  some  cases  lived  an  equal  period, 
indicating  that  both  were  equally  abnormal  and  that  the  discrepancy  must 
be  sought  elsewhere.  Forel  long  ago  criticized  Graber's  results  because  of 
the  strong  odors  employed,  insisting  that  natural  odors  to  which  the  various 
insects  are  accustomed  should  be  used,  and  this  objection  may  hold  in  some 
measure  for  the  essential  oils.  Moreover,  it  seems  possible  that  reaction- 
time  experiments  do  not  furnish  such  decisive  tests  as  those  made  by  Forel, 
Hauser,  Mayor,  and  others.  Furthermore,  the  use  of  a  stop-watch  would 
appear  almost  imperative,  especially  for  short  intervals. 

Mclndoo  frequently  finds  a  relation  between  the  number  of  pores  and 
the  reaction-time.  "If  the  reaction-time  of  each  caste  of  the  honey-bee 
is  compared  with  the  total  number  of  olfactory  pores,  a  consistent  ratio  is 
obtained.  A  drone  has  2,600  pores  and  responds  in  2.9  seconds;  a  worker 
posesses  2,200  pores  and  responds  in  3.4  seconds,  and  a  queen  has  1,800 
pores  and  responds  in  4.9  seconds."  This,  however,  is  only  a  qualitative 
relation,  since  the  worker  with  400  pores  less  than  the  drone  requires  but 
0.5  second  longer,  while  the  queen  with  800  pores  less  takes  2  seconds 
longer.  The  absence  of  a  definite  quantitative  relation  is  further  shown 
by  the  fact  that  removing  the  wings  of  workers  with  1,510  pores  increased 
the  reaction-time  8  times,  while  coating  the  658  pores  of  the  legs  increased 
it  but  2.5  times.  Finally,  although  wasps  are  generally  regarded  as  having 
a  keener  sense  of  smell  than  bees,  the  one  species  studied  possessed  only 
1,957  pores. 

On  theoretical  grounds  it  is  difficult  to  reconcile  the  large  number  of 
pores  and  their  distribution  with  the  high  development  of  the  sense  of 
smell  in  insects.  This  is  often  much  more  highly  developed  than  vision, 
and  one  would  expect  a  highly  differentiated  organ  to  correspond  and  one  in 
immediate  connection  with  the  "brain,"  as  is  the  compound  eye.  On  the 
contrary,  there  are  hundreds  of  pores,  some  of  them  as  far  away  from  the 
central  ganglion  as  possible  and  several  times  as  far  as  others.    Moreover, 


232  PRINCIPLES  AND   CONCLUSIONS. 

their  position  on  the  tarsi  and  the  sting  casts  grave  doubt  upon  their  effec- 
tiveness as  olfactory  pores.  Their  localization  on  the  bases  of  the  wings, 
the  legs,  and  the  sting  suggests  that  they  have  to  do  with  the  sense  of  touch 
or  feel  in  the  wide  sense  and  that  their  response  to  chemical  stimuli  is 
somewhat  similar  to  that  of  all  exposed  nerve-ends  *  However,  it  is  idle  to 
speculate  upon  this  until  the  results  of  new  investigations,  which  take 
into  account  the  experiments  of  both  Mclndoo  and  his  predecessors,  are 
made  available. 

Turner  (1916:385)  states:  "These  experiments  of  Mclndoo  are  pains- 
taking and  his  anatomical  studies  of  what  he  calls  olfactory  pores  are 
excellent,  but  the  serious  student,  who  is  acquainted  with  the  experiments 
of  Forel  and  others  who  'claim  that  the  antennae  are  the  organs  of  smell' 
will  not  be  convinced  that  the  last  word  has  been  said  on  the  subject. 
They  do  not  seem  to  have  met  the  criticisms  raised  by  Forel"  (1878,  1886, 
1908),  as  indicated  above. 

INTELLIGENCE. 

Relation  between  the  senses  and  mental  faculties  of  insects. — 

Forel  (1886:233)  considered  that  insects  possess  our  five  senses,  with  the 
possible  exception  of  hearing,  in  a  well-differentiated  degree  and  with  a 
special  energy  that  we  consider  analogous  to  our  own.  The  quality  of  their 
vision  is  different  from  that  of  ours  in  certain  respects,  as  certain  of  them 
see  the  ultra-violet  rays.  Many  insects  have  besides  a  kind  of  odor  by 
contact,  which  enables  the  ants  in  particular  to  distinguish  their  companions 
from  enemies.  The  development  of  each  sense  and  of  each  of  its  kinds  of 
special  energy  (color,  odor)  varies  enormously,  not  only  for  families  and 
genera,  but  even  with  related  species  and  with  the  sexes  of  the  same  species. 
Insects  naturally  combine  their  different  senses  in  their  acts,  but  in  general 
the  principal  sense  is  that  of  direction,  just  as  sight  is  with  man.  Sight 
assumes  this  role  with  the  aerial  insects,  especially  the  dragon-flies  and  the 
butterflies.  With  the  workers  among  ants,  it  is  in  general  smell,  with  the 
spiders,  touch,  and  with  the  beetles  it  is  touch  and  taste  combined. 

It  is  evident  that  insects  possess  the  faculty  of  the  so-called  voluntary 
movements  which  are  not  merely  reflex  or  simply  automatic,  but  very 
well  coordinated  and  nearly  all  dictated  by  combinations  of  instinctive 
reason  with  the  aid  of  sensory  impressions,  and  admirably  adapted  to  their 
end.  They  frequently  have  an  excellent  memory  of  places,  of  things,  and 
perhaps  of  persons.  Thus,  insects  reason,  and  the  most  intelligent  of  them, 
the  social  Hymenoptera,  reason  much  more  than  one  thinks  when  he  ob- 
serves the  mechanism  due  to  instinct,  but  to  properly  observe  and  compre- 
hend these  reasoning  processes,  it  is  necessary  to  put  instinct  out  of  com- 
mission. Instinct  is  organized,  systematized,  and  automatic  reasoning, 
that  is,  it  has  become  unconscious.  Instinct  and  reason  are  not  in  inverse 
proportion  to  each  other,  as  Pouchet  has  remarked,  and  the  insects  with  the 
most  intelligence  are  generally  those  with  the  largest  number  of  varied 
instincts,  though  this  is  not  always  true.  Finally,  insects  exhibit  passions 
that  are  more  or  less  bound  up  with  their  instincts,  and  these  vary  enor- 

*  Since  this  was  written,  it  has  been  found  that  Graber  ascribed  the  sensitiveness  of  the 
"afterborsten  "  and  the  legs  to  relatively  strong  odors  to  the  sense  of  feel  and  not  to  that  of 
smell. 


INTELLIGENCE.  233 

mously  with  the  species.  Among  the  ants  the  traits  of  character  recogniza- 
ble are  anger,  hate,  devotion,  activity,  perseverance,  greediness,  boldness, 
discouragement,  and  fear.  Thus,  in  studying  the  habits  of  insects  it  is 
necessary  to  take  into  consideration  their  mental  faculties  as  well  as  their 
organs  of  sense. 

Memory  and  general  intelligence  of  wasps. — The  Peckhams 
(1887:121)  concluded  that  wasps  have  a  very  good  memory,  remembering 
for  ten  days  the  characteristics  of  the  glass  of  a  window  through  which 
they  were  accustomed  to  fly.  The  memory  varied  greatly  in  different  indi- 
viduals; in  the  color  experiments  many  wasps  would  fly  into  the  false 
entrance  several  times,  while  others  would  fly  in  but  once,  and  still  others 
would  only  hover  over  it  before  turning  to  the  true  opening.  When  blades 
of  grass  were  placed  across  the  entrance  to  the  nest,  not  one  of  more  than 
300  wasps  made  any  attempt  to  remove  them,  in  spite  of  the  fact  that  they 
seriously  hindered  them  and  were  less  than  a  usual  load  in  weight.  Even 
when  going  out  without  loads  no  endeavor  was  made  to  get  rid  of  the  ob- 
stacle. They  noted  two  classes  of  intelligent  action  among  the  Hymen- 
optera,  which  are  sufficiently  distinct  to  be  considered  separately  (1905:301). 
The  first  includes  those  acts  performed  by  large  numbers  in  a  similar 
fashion  under  like  conditions,  while  in  the  second  each  act  is  an  individual 
affair.  The  first  is  exemplified  by  Fabre's  experiment  with  Osmia,  in  which 
he  took  2  dozen  nests  in  shells  from  a  quarry,  where  the  bees  had  been 
nesting  for  centuries,  and  placed  them  in  his  study  along  with  some  empty 
shells  and  hollow  stems.  When  the  bees  came  out  in  the  spring,  nearly  all 
chose  the  stalks  as  better  suited  to  build  in  than  the  shells,  thus  evidencing 
an  intelligent  adaptation  to  new  conditions.  The  second  case  is  illustrated 
by  a  wasp  {Pompilus  scelesius)  which  tried  to  drag  its  prey  into  the  opening  of 
a  nest  that  was  too  small.  After  several  vain  tugs,  it  was  carried  to  a  place 
of  safety  up  among  some  clover  blossoms,  and  after  some  fifteen  minutes 
of  walking  and  brushing  herself,  the  wasp  set  about  making  the  hole  larger. 
During  this  period  she  must  have  carried  in  mind  the  idea  of  doing  a  neces- 
sary act  outside  of  the  ordinary  routine,  and  it  is  also  suggestive  that  the 
hole  when  enlarged  was  exactly  what  was  needed. 

Memory  of  place  in  bees. — In  an  extended  critique  of  Bethe's  paper 
(1898: 15)  which  endeavored  to  establish  the  hypothesis  that  bees  are  merely 
reflex  machines,  Buttel-Reepen  (1900:96,  1907)  discussed  the  evidence 
chiefly  under  three  heads,  namely,  (1)  the  hive  odor  and  the  reactions 
resulting  from  it,  (2)  the  means  of  communication  in  bees,  and  (3)  memory 
of  place  in  bees.  The  latter  alone  is  directly  connected  with  the  present 
inquiry  and  hence  summarized  here.    Bethe  assumed  that — 

"Bees  are  led  back  to  the  hive  by  a  force  entirely  unknown  to  us.  This  force  does 
not  adhere  to  the  hive  itself,  and  it  does  not  lead  bees  back  to  the  hive  itself,  but  to 
the  place  in  space  which  the  hive  usually  occupies.  It  does  not  act  at  boundless 
distances.  It  is  an  old  experience  of  bee-keepers  that  they  can  take  a  colony  to  another 
stand  without  fearing  that  the  bees  will  return  to  the  old  place,  if  the  new  spot  is 
only  more  than  six  kilometers  from  the  old.  It  follows,  then,  that  this  force  acts  at 
most  at  a  distance  of  six  kilometers,  since  the  impulse  to  return  to  the  hive  is  the  strong- 
est of  all  impulses  in  bees.    But  I  believe  that  the  zone  of  action  of  the  force  is  not  a 


234  PRINCIPLES   AND   CONCLUSIONS. 

circle  with  a  radius  of  six  kilometers,  but  of  only  three  or  four  kilometers.  If  the  cir- 
cle had  had  a  radius  of  six  kilometers,  then  the  bees  of  the  transposed  hive  would 
be  back  into  the  circle  of  action  if  they  got  more  than  half  that  distance  near  the  old 
position  in  foraging,  and  would  have  to  return  to  the  old  place.  But  this  only  happens 
if  the  old  position  is  less  than  six  kilometers  away  from  the  new.  We  must,,  therefore, 
accept  something  near  three  kilometers  as  the  boundary  for  this  circle  of  action  for 
this  force." 

When  Bethe  freed  8  marked  bees  at  each  of  three  distances  from  the  hive, 
namely,  350,  400,  and  650  meters,  they  found  their  way  back  in  1.5  to  3.5, 
5  to  10,  and  4.75  to  10.5  minutes  respectively.  Buttel  pointed  out  that  at 
the  normal  velocity  for  bees,  doubled  because  they  were  carrying  loads, 
the  unknown  force  should  have  led  them  all  back  in  1  minute  12  seconds, 
1  minute  36  seconds,  and  2  minutes  36  seconds,  for  the  respective  distances. 
This  discrepancy  can  only  be  explained  on  the  assumption  that  the  bees 
had  to  orient  themselves  with  their  eyes  and  that  they  made  errors  in  doing 
so,  and  thus  lost  time.  Since  the  unknown  force  does  not  bring  bees  back 
to  the  hive  but  only  to  the  place  where  it  stands  or  usually  stood,  it  must  be 
memory  of  location.  When  bees  are  stupefied  with  chloroform,  ether, 
saltpeter,  etc.,  memory  of  location  entirely  disappears,  and  they  no  longer 
recognize  their  home  or  the  place  where  it  stands.  As  soon  as  they  become 
normal,  they  again  begin  to  orient  themselves  with  regard  to  the  home, 
gathering  new  memory  pictures  of  the  sources  of  nectar  and  pollen  as  well  as 
of  the  new  hive.  This  also  shows  their  capacity  for  learning,  a  fact  disputed 
by  Bethe.  Buttel  also  emphasizes  the  discrepancy  between  Bethe 's  as- 
sumption that  all  the  bees  set  free  within  the  circle  of  action  of  the  "un- 
known force"  must  return  to  the  place  that  "draws  them  like  a  magnet," 
and  the  actual  results  obtained  by  him  in  the  box  experiment.  When  the 
bees  were  released  from  the  box,  most  of  them,  after  a  few  circles  in  the  air, 
went  in  the  direction  of  the  institute,  but  "two  mounted  to  a  height  of 
about  3  meters,  made  a  few  circles  of  4  or  5  meters  in  diameter,  and 
then  alighted  on  the  box.  I  drove  them  away  into  the  air  again.  They 
flew  in  large  circles  about  it,  and  then  again  alighted  on  the  box.  I  then 
took  the  box  away  and  put  it  on  another  stone,  having  driven  the  bees  into 
the  air  once  more.  Both  bees  flew  so  high  that  I  could  no  longer  see  them, 
but  a  few  seconds  later  they  reappeared  and  slowly  flew  about  the  place 
where  the  box  had  stood."  Thus  some  bees  were  influenced  by  the  "un- 
known force"  and  others  were  not,  a  fact  that  Bethe  did  not  attempt  to 
explain.  Buttel  carried  out  similar  experiments  with  the  same  results  and 
all  of  them  furnished  evidence  of  memory  for  locality,  though  he  regarded 
the  conditions  as  abnormal  in  comparison  with  those  carried  on  at  the 
apiary.  Although  Bethe  gave  no  explanation  of  why  the  "unknown  force" 
operates  at  a  distance  of  but  3  or  4  km.,  it  is  really  very  simple,  since 
this  supposedly  mysterious  force  operates  only  within  the  space  in  which 
the  bees  have  made  flights  of  orientation  and  stored  up  memory  pictures. 

The  identity  of  this  unknown  force  with  memory  of  location  is  further 
proved  by  the  following  facts:  If  young  bees  are  let  fly  not  far  from  the 
apiary  before  they  have  had  their  flight  of  orientation,  none  of  them  find 
their  way  back  to  the  hive,  but  if  old  bees  are  released  at  a  much  greater 
distance  they  all  return.     If  a  colony  is  brought  from  a  place  more  than 


INTELLIGENCE.  235 

7  kilometers  away  and  the  old  bees  released  only  30  or  40  meters  from  the 
hive  before  they  have  been  able  to  make  their  flight  of  orientation,  none 
find  their  way  back  in  case  trees  or  houses  intervene.  Memory  of  locality 
may  be  lost  through  artificial  swarming,  by  the  influence  of  buckwheat 
honey;  by  the  effect  of  dark  or  cold;  by  throwing  bees  into  water,  and  by 
the  lapse  of  time.  Memories  also  disappear  quickly  by  new  impressions 
obliterating  the  old.  In  their  first  flight  from  the  hive,  bees  turn  their 
heads  toward  the  latter  and  survey  the  hive,  the  neighboring  hives,  and 
the  general  surroundings.  After  this  short  preliminary  flight,  small  and 
then  larger  orientation  flights  are  taken  and  the  landmarks  impressed  on 
the  memory.  It  is  evident  that  bees  also  orient  themselves  in  special  ways. 
If  the  height  of  a  hive  is  changed  so  that  the  entrance  is  suddenly  made 
30  cm.  higher  or  lower,  the  bees  fly  exactly  to  the  level  where  the  entrance 
was  before,  and  hours  or  even  days  pass  before  a  smooth  flight  is  made  to 
the  new  height.  The  ability  to  judge  distances  even  goes  so  far  that  bees 
normally  fly  in  and  out  of  the  same  corner  of  the  hive-entrance.  If  the 
entrance  is  closed  to  about  the  breadth  of  an  inch,  they  will  try  to  enter 
at  the  usual  spots  and  find  the  open  part  only  after  considerable  search. 
A  bee  flies  to  the  point  of  entrance  without  being  able  to  see  it  or  the  nearest 
surroundings  of  the  entrance,  on  the  basis  of  its  orientation  in  the  neigh- 
borhood. As  it  comes  closer,  it  generally  notices  the  surroundings  of  the 
entrance,  for  it  becomes  aware  of  any  changes  in  the  outside  of  the  hive. 

Forel  (1900,  1908:217)  has  dealt  with  Bethe's  results  and  conclusions 
in  similar  detail.    He  says  : 

"When  writing  the  preceding,  I  was  ignorant  of  the  work  of  Buttel-Reepen.  If 
on  the  one  hand  I  regret  it,  on  the  other  it  has  the  advantage  of  having  rendered  my 
criticism  of  Bethe  independent  of  his,  and  the  reader  of  both  will  be  astonished  to 
see  to  what  extent  our  results  agree. 

"I  am  obliged  to  combat  Bethe's  conclusions  as  preconceived,  one-sided,  and  of 
an  absolutism  quite  contrary  to  logic  and  the  scientific  spirit." 

Memory  of  time  and  association  of  impressions. — Buttel-Reepen 
stated  that  where  colonies  stand  in  fields  of  buckwheat  the  flight  is  lively 
until  about  10  o'clock,  then  becomes  entirely  quiet  for  the  rest  of  the  day, 
to  begin  again  vigorously  the  next  morning.  Buckwheat  nectar  is  abun- 
dant only  in  the  early  morning;  as  the  nectaries  dry  up,  the  bees  fly  out 
once  or  twice  and  then  cease  their  vain  flight.  In  spite  of  the  sea  of  flowers 
and  the  strong  fragrance,  few  bees  are  found  in  the  field  after  10  o'clock. 
Regardless  of  the  constant  attraction  of  color  and  scent  and  the  habit  of  daily 
flight  to  the  fields,  the  processes  of  learning  and  remembering  play  the 
directive  role. 

Association  of  impressions  is  illustrated  by  the  behavior  of  bees  that  found 
a  honeycomb  in  a  room,  after  flying  through  the  open  window.  More  and 
more  came,  some  of  them  being  kept  out  at  the  second  window,  which  was 
closed.  To  prevent  this  the  honeycomb  was  placed  in  the  open  window,  and 
a  half-hour  later  the  bees  were  driven  away  and  the  window  closed.  Twenty 
minutes  later  the  room  above,  the  windows  of  which  were  open,  was  found 
full  of  bees.  In  order  to  observe  their  behavior  accurately,  the  bees  were 
driven  out,  the  windows  closed,  and  Buttel  went  into  the  garden.  Here 
the  bees  were  seen  trying  to  enter  at  the  window  from  which  they  had  been 


236  PRINCIPLES  AND   CONCLUSIONS. 

fed,  then  flying  to  the  next  window  and  afterward  to  the  other  windows  until 
they  had  tried  them  all.  It  was  then  assumed  that  the  existence  of  an 
actual  association  of  honey  with  the  form  of  a  window  would  lead  them  to 
extend  the  search  to  the  neighboring  house,  which  they  did.  He  also  cited 
in  confirmation  the  observation  that,  when  a  dish  of  honey  is  placed  on  the 
trunk  of  a  tree,  bees  afterward  search  for  honey  at  the  same  place  on  all 
the  trees  in  the  neighborhood. 

Memory  of  time  and  memory  association  in  honey-bees. — Forel 

(1907:459)  reported  the  behavior  of  bees  which  were  led  to  visit  an  out-door 
dining  table,  on  which  it  was  the  habit  to  place  preserves  at  breakfast, 
from  7h30m  to  9h30m  a.  m.,  and  at  tea,  from  4  to  5  p.  m.  Drawn  by  the  odor 
of  cooked  cherries,  one  or  two  bees  first  found  the  preserves  and  in  a  day 
or  two  a  whole  swarm  came  to  feast  on  them.  However,  after  having  sought 
for  them  at  mid-day  also  and  having  found  nothing,  they  entirely  ceased 
coming  at  this  time  and  confined  their  visits  to  the  hours  of  breakfast  and 
tea.  After  this  habit  had  been  confirmed,  the  table  was  set  as  for  breakfast, 
but  no  preserves  were  placed  on  it.  A  large  number  of  bees  came  to  it  as 
usual  and  searched  everything  in  vain.  They  stopped  coming  at  10  o'clock 
and  only  a  single  one  appeared  at  noon  and  but  one  or  two  at  4  o'clock. 
The  next  morning  a  much  smaller  number  than  usual  was  observed  and 
they  did  not  stay  long.  More  appeared  at  noon  than  before,  as  if  driven  to 
make  the  search  for  the  sweets  at  other  hours.  When  they  returned  at 
4  o'clock  they  were  given  some  preserves,  and  this  led  others  to  come.  The 
next  day  the  same  behavior  occurred  at  breakfast  time,  the  bees  flying 
against  an  inverted  glass  containing  preserves  but  paying  no  attention  to 
the  edge  where  the  odor  could  be  perceived.  At  10  o'clock  all  had  again 
disappeared.  After  several  days  a  supply  of  sirup  and  preserves  was  made 
constantly  available,  and  the  bees  ceased  to  come  at  stated  hours.  These 
facts  were  regarded  as  clearly  proving  that  bees  not  only  have  place  memory 
but  also  that  of  time.  In  short,  they  returned  to  the  same  place  and  ex- 
amined the  same  or  similar  objects  only  at  the  hours  when  they  had  found 
them  before,  and,  after  several  deceptions,  but  once  at  mid-day,  the  hour 
at  which  they  found  nothing.  Bees  were  found  peculiarly  adapted  to  the 
experiment  on  account  of  their  poor  sense  of  smell,  visual  and  gustatory 
memory  operating  alone.  The  visual  memory  of  colors  and  forms  guided 
them  and  also  enabled  them  to  distinguish  the  preserve  container  and 
similar  objects,  the  sense  of  smell  coming  into  action  at  the  very  short 
distance  of  1  cm. 

Intelligence  of  honey-bees. — In  his  conclusions  (1907:44)  Buttel- 
Reepen  stated: 

"It  is  unquestionable  to  me  that  the  senses  of  bees  are  similar  to  those  of  men,  and 
that  especially  the  senses  of  sight,  hearing,  and  smell  play  an  important  part.  As 
Wundt  has  already  shown,  we  certainly  are  'referred  essentially  to  outer  observations 
in  animals;  what  they  teach  us  is  not  a  total  dissimilarity  in  the  capacity  of  mind, 
but  the  most  essential  conformity  with  the  psychic  processes  that  we  observe  in  man, 
and  know  chiefly  from  observation  of  ourselves.'  The  anthropomorphic  apprehen- 
sion relative  to  the  question  of  consciousness  has  brought  it  about  that  there  has  been 
ascribed  to  bees  a  consciousness  similar  to  human  consciousness,  and  accordingly 


INTELLIGENCE.  237 

the  most  varied  human  feelings.  On  the  basis  of  my  observations  I  am  of  the  opinion 
that  bees  possess  either  no  consciousness  at  all,  or  one  of  only  the  lowest  degree  of 
development.  The  question  of  consciousness  is  left  to  subjective  estimates,  but  the 
question  whether  an  animal  learns  and  can  acquire  experience  or  not  may  be  deter- 
mined objectively.  We  see  that  bees  show  signs  of  an  admirable  memory  in  their 
orientation  and  also  in  other  activities;  further  I  believe  I  have  shown  that  the 
bee  possesses  a  perception  for  color  and  form,  and  develops  a  rich  capacity  for  com- 
munication by  means  of  its  well-developed  'language';  that,  further,  it  is  able  to 
gather  experiences,  to  learn  and  to  form  associations  of  impressions,  etc.  I  can  not 
agree  with  Bethe,  therefore,  in  his  denial  that  the  bee  has  capacity  to  gather  expe- 
rience and  thereby  to  modify  its  action.  The  bee  is  evidently  much  more  than  a  reflex 
machine." 

The  psychic  powers  of  insects. — Forel  summed  up  his  conclusions  as 
to  the  intelligence  of  insects  as  follows  (1901:25;  1904:20;  1908): 

"It  ensues  from  the  concordant  observations  of  all  the  experts  that  sensation, 
perception,  association,  inference,  memory,  and  habit  in  the  social  insects  follow  the 
same  fundamental  laws  as  in  the  vertebrates  and  ourselves.  Moreover,  attention 
is  strikingly  developed  in  insects,  often  assuming  the  nature  of  an  obsession  that  is 
hard  to  divert.  On  the  other  hand,  inherited  automatism  manifests  an  immense 
preponderance,  and  the  faculties  mentioned  are  exhibited  in  but  exceedingly  feeble 
form  beyond  the  limits  of  the  instinct-automatism  fixed  in  the  species. 

"The  senses  of  insects  are  our  own.  Only  the  sense  of  hearing  remains  doubtful 
in  so  far  as  its  location  and  interpretation  are  concerned.  A  sixth  sense  has  not  yet 
been  shown  to  exist,  and  a  special  sense  of  direction  and  orientation  is  certainly 
lacking.  Reflexes,  instincts,  and  plastic  individually  adaptive  central  nervous  activ- 
ities pass  over  into  one  another  by  gradations.  Without  becoming  antagonistic, 
the  central  nervous  activity  in  the  different  groups  and  species  of  animals  becomes 
complicated  in  two  fashions:  (1)  through  inheritance  by  natural  selection,  etc., 
of  complex  purposeful  automatic  responses,  or  instincts;  (2)  through  the  manifold 
possibilities  of  plastic,  individually  adaptive  activities,  in  combination  with  the  faculty 
of  gradually  developing  secondary  individual  automatic  responses,  or  habits.  In  social 
insects  the  correlation  of  more  developed  psychic  powers  with  the  volume  of  the  brain 
may  be  directly  observed.  In  these  animals  it  is  possible  to  demonstrate  the  existence 
of  memory,  associations  of  sensory  images,  perception,  attention,  habits,  simple 
powers  of  inference  from  analogy,  the  utilization  of  individual  experiences  and  hence 
distinct,  though  feeble,  plastic  individual  deliberations  or  adaptations. 

"It  is  also  possible  to  detect  a  corresponding,  simpler  form  of  volition,  i.  e.,  the 
carrying  out  of  individual  decisions  in  a  more  or  less  protracted  time  sequence,  through 
different  concatenations  of  instincts;  furthermore  different  kinds  of  discomfort  and 
pleasure  emotions,  as  well  as  interaction  and  antagonisms  between  these  diverse 
psychic  powers.  In  insect  behavior  the  activity  of  the  attention  is  one-sided  and 
occupies  a  prominent  place.  It  narrows  the  scope  of  behavior  and  renders  the  animal 
temporarily  unresponsive  to  other  sense-impressions. 

"Even  to-day  I  am  compelled  to  uphold  the  seventh  thesis  which  I  established  in 
1877  in  my  habilitation  as  privat-docent  in  the  University  of  Munich:  'All  the  prop- 
erties of  the  human  mind  may  be  derived  from  the  properties  of  the  animal  mind.' 
I  would  merely  add  to  this:  'And  all  the  mental  attributes  of  higher  animals  may  be 
derived  from  those  of  lower  animals.'  In  other  words:  The  doctrine  of  evolution  is 
quite  as  valid  in  the  province  of  psychology  as  it  is  in  all  the  other  provinces  of  organic 
life.  Notwithstanding  all  the  differences  presented  by  animal  organisms  and  the 
conditions  of  their  existence,  the  psychic  functions  of  the  nerve-elements  seem  never- 
theless to  be  everywhere  in  accord  with  certain  fundamental  laws,  even  where  this 
would  be  least  expected  on  account  of  the  magnitude  of  the  differences." 


238  PRINCIPLES  AND  CONCLUSIONS. 

GENERAL  RESUME. 

TREATMENT. 

Plateau  focussed  attention  so  exclusively  upon  attraction  that  it  has 
remained  the  chief  theme  of  experimental  pollination  for  45  years.  While  the 
present  series  of  studies  has  endeavored  to  deal  with  the  whole  field  in  a 
more  comprehensive  fashion,  attraction  is  necessarily  the  central  theme  of 
a  resume  that  attempts  to  summarize  all  the  experimental  results  in  brief. 
This  is  considered  with  respect  to  color,  odor,  form  and  size,  distant  and  near 
attraction,  and  competition.  The  first  is  discussed  under  the  captions  of 
mutilation,  artificial  flowers,  painted  flowers,  inclosing  in  glass,  green  and 
showy  nectarless  flowers,  color  preference,  and  the  second  under  those 
of  masking  and  concealing  flowers,  honey,  perfumes  and  scents,  and  relative 
values.  The  remaining  major  divisions  are  learning  and  habit,  memory 
and  intelligence.  For  the  treatment  of  these  there  is  much  less  definite 
and  accurate  experimental  material,  and  an  adequate  exposition  of  them 
must  await  extensive  experimentation  under  the  quantitative  conditions 
afforded  by  control  and  measurement. 

ATTRACTION. 

COLOR. 

Mutilation. — Here  it  is  necessary  to  take  into  account  only  those  ex- 
periments in  which  the  corolla,  perianth,  ray-flowers,  or  bracts  were  removed 
or  reduced  in  expanse  by  shortening  or  otherwise.  Covering  the  attractive 
part  produced  essentially  the  same  effect,  but  such  cases  are  considered 
under  masking  or  artificial  flowers  in  accordance  with  the  device  employed. 
In  Plateau's  first  experiments  with  decorollate  flowers  (1896),  his  results 
in  general  failed  to  confirm  his  conclusion  as  to  the  insignificant  role  of  the 
corolla  in  attraction.  In  the  case  of  several  species  of  flowers  and  insects, 
the  mutilated  flowers  were  visited  less  than  the  normal,  for  example, 
24:44,  4: 10,  250:330,  and  16  inspections  to  29,  and  in  others  no  comparison 
was  possible  because  the  visits  to  normal  flowers  were  not  noted.  More- 
over, no  account  was  taken  of  habit  and  the  effect  of  removing  the  corolla 
on  the  diffusion  of  the  odor,  especially  of  the  nectar.  In  the  studies  of 
decorollate  poppies  (19023),  he  obtained  an  average  of  4.5  visits  to  the  mu- 
tilated flowers  to  3.4  for  the  normal.  These  were  wholly  exceptional  and 
are  negatived  by  the  results  of  all  other  workers.  They  serve  to  illustrate 
the  variations  in  behavior  that  may  be  expected,  but  in  this  case  they  are 
doubtless  to  be  explained  on  the  basis  of  habit  and  accessibility. 

In  working  with  decorollate  poppies  and  geraniums  (1904),  Giltay 
regularly  obtained  such  ratios  between  normal  and  mutilated  flowers  as 
96:9,  and  38:1,  while  in  the  later  studies  of  1906,  the  intact  flowers  were 
always  much  more  visited  likewise.  On  the  second  day  of  an  installation, 
the  ability  of  the  bees  to  learn  changed  such  ratios  as  15:0  and  12:0  to 
18:13,  but  they  were  rarely  if  ever  reversed.  Similarly,  Schroder  (1901) 
secured  ratios  of  37:0  and  21:4  with  Syritta  pipiens  on  the  first  day,  but  by 
the  second  day  experience  increased  the  visits  to  the  mutilated  to  almost 
half,  viz,  19  to  46.  Andreae  (1903)  found  decorollate  flowers  to  be  several 
times  less  attractive  than  normal  ones  (3 :  24),  and  Errera  (1904),  about  half  as 


GENERAL  RESUME.  239 

attractive  (24:46).  Wery  (1904)  regularly  obtained  more  visits  to  the  normal 
flowers ;  the  difference  was  often  small  with  a  heterogeneous  group  of  visitors, 
such  as  19 :  13,  27 :  24, 43 :  27,  but  when  the  honey-bees  alone  were  counted  the 
ratios  were  1 1 : 6,  29 :  10,  and  20 : 6.  The  totals  for  one  series  was  138  normal 
and  46  mutilated  for  all  visitors,  and  72  to  28  for  the  bees.  Detto  (1905) 
observed  that  the  removal  of  the  corolla  stopped  visits  completely,  and 
that  replacing  the  petals  caused  them  to  be  resumed.  Lovell  (1909)  secured 
decisive  results  as  a  rule  by  the  removal  of  the  corolla,  as  shown  by  the 
following  ratios  for  normal  and  mutilated,  15:0,  12:0,  7:0,  and  12:1. 
In  Allard's  experiments  (1911)  the  loss  of  the  corolla  caused  the  inspections 
to  drop  from  81  to  4,  while  a  single  petal  received  16  inspections  to  26  for 
the  normal.  Placing  a  single  petal  on  a  decorollate  flower  yielded  8  inspec- 
tions to  9  for  such  a  petal  pinned  to  a  stem  and  27  for  the  normal;  replacing 
the  petals  regularly  brought  the  inspections  back  to  the  usual  number. 

In  the  present  studies,  the  removal  of  the  corolla  has  rarely  eliminated 
visitors  entirely,  but  it  has  usually  decreased  them  from  three  to  ten  times, 
depending  upon  the  flower  and  the  habit  of  the  visitors.  Reducing  the 
size  of  the  corolla  was  somewhat  less  effective  as  a  rule,  the  decrease  ranging 
from  a  half  to  a  tenth.  With  both  lips  removed  in  Monarda,  visits  were 
reduced  to  a  fortieth  of  the  total  for  all  mutilations  and  with  the  lower 
lip  gone,  to  a  tenth.  The  most  striking  exception  occurred  in  Chamae- 
nerium,  where  the  excision  of  all  the  flower  parts  but  the  ovary  and  nectar 
ring  resulted  in  nearly  5  times  as  many  visitors  and  visits  as  to  the  normal. 
This  was  apparently  due  to  the  marked  effect  of  habit  in  responses  to  this 
flower,  as  well  as  to  the  exposure  of  the  nectar.  This  probably  also  explains 
the  discrepancy  involved  in  Detto's  results,  in  which  the  reduction  of  the 
corolla  was  without  effect.  Experiments  with  newly  hatched  insects  will 
be  required  to  evaluate  the  effect  of  habit,  but  practically  all  the  existing 
experimental  results  are  in  accord  in  demonstrating  that  the  loss  or  re- 
duction of  the  corolla  has  a  significant  and  usually  a  decisive  effect  in  de- 
creasing visitors  and  visits.  This  applies  with  greatest  force  to  the  bees, 
and  is  somewhat  modified  by  the  type  of  flower  and  especially  its  fragrance. 

Artificial  flowers. — Plateau  devoted  four  papers  to  the  attraction  exerted 
by  artificial  flowers,  in  which  he  insisted  upon  the  perfection  of  his  imitations 
and  ascribed  the  abundant  visits  obtained  by  other  investigators  to  the 
presence  of  materials  attractive  by  their  odor  or  to  imperfections  in  the 
method.  Neither  the  presence  of  attractive  substances  nor  the  effect  of 
habit  can  explain  the  frequent  initial  visits  obtained  by  the  great  majority 
of  workers,  and  the  proper  explanation  seems  to  be  that  of  the  variation 
to  be  expected  in  consequence  of  differences  in  time,  place  or  installation. 
In  his  preliminary  studies  (1877),  Plateau  obtained  few  visits  to  artificial 
flowers  and  these  were  made  chiefly  by  butterflies,  but  visits  and  inspections 
were  much  more  numerous  in  the  experiments  of  1897,  though  as  a  rule 
far  below  those  to  normal  flowers.  Bombus  gave  4  inspections  out  of  10 
to  imitations,  Anthidium  11  out  of  38,  and  Megachile  10  out  of  17;  in  some 
cases  of  those  reported  in  the  series  of  1906,  artificial  flowers  received  as  many 
as  8  visits  and  7  inspections  to  15  visits  to  normal  ones.  Forel  agreed  with 
Plateau's  conclusions  as  to  the  ineffectiveness  of  artificial  flowers,  but 
his  results  likewise  were  not  at  all  in  harmony  with  each  other.     Bees  dis- 


240  PRINCIPLES   AND   CONCLUSIONS. 

dained  imitations  placed  in  the  midst  of  dahlias,  but  visited  artefacts 
of  Petunia  and  Hieracium.  Moreover,  it  proved  possible  to  train  bees  to 
come  to  artificial  flowers  and  ignore  the  dahlias. 

Reeker  (1898)  found  that  artificial  flowers  were  visited  so  regularly  and 
frequently  when  placed  at  6  to  12  meters  from  the  natural  ones  that  he 
found  it  undesirable  to  carry  his  experiments  further,  and  Schroder  (1901) 
induced  Syritta  to  visit  them  almost  as  abundantly  as  the  normal  by  the 
addition  of  honey.  In  an  admirable  series  of  experiments  that  rivaled  those 
of  Plateau,  Andreae  (1903)  obtained  numerous  visits  to  artificial  flowers, 
in  one  instance  81  visits  being  made  to  the  latter  and  but  56  to  the  normal. 
In  the  competition  between  color  and  odor  as  represented  by  artificial 
flowers  on  one  hand  and  masked  natural  ones  on  the  other,  the  results  were 
uniformly  in  favor  of  the  former,  as  shown  by  such  ratios  as  55 : 1,  41 : 0,  31 : 1, 
and  28:3.  Wery's  results  (1904)  were  equally  conclusive,  the  artificial 
flowers  often  equaling  or  exceeding  the  normal  ones  in  attractiveness  and 
regularly  surpassing  honey  in  this  respect.  They  attracted  honey-bees 
readily  and  to  the  same  degree  as  normal  flowers  placed  in  a  globe.  Lovell 
(1912)  employed  dry  yellow  immortelles  in  competition  with  honey,  and 
obtained  three  times  as  many  visits  to  them  as  to  the  latter.  Allard  (1911) 
found  that  the  placing  of  cloth  petals  over  the  natural  ones  of  cotton  usually 
decreased  inspections,  but  a  crepe-paper  blossom  of  the  proper  color  received 
3  inspections  to  8  for  the  normal.  Detto  (1905)  also  found  that  replacing 
the  corolla  with  one  of  yellow  paper  stopped  visits,  which  began  again  as 
soon  as  the  petals  were  replaced.  On  the  other  hand,  flowers  with  a  ring 
of  colored  paper  were  readily  visited. 

In  the  present  experiments  artificial  flowers  were  visited  about  an  eighth 
as  much  as  natural  ones.  In  more  than  half  the  installations  they  were 
completely  ignored  or  visited  but  little.  In  several  instances  the  total 
number  of  visits  to  imitations  was  large,  though  the  ratio  rarely  reached 
one-half.  The  highest  relative  number  of  visits  was  in  the  case  of  a  Frasera 
supplied  with  Campanula  petals,  namely,  56:97,  but  this  was  doubtless 
owing  to  the  naturalness  of  the  living  tissue.  The  fact  that  Bombus  went 
readily  to  paper  Mentzelias  before  the  natural  ones  were  open  appears  to 
prove  that  the  paper  flowers  were  not  repellent  in  themselves,  but  that  the 
habit  response  to  the  natural  flowers  was  a  very  definite  one,  as  would  be 
expected.  While  our  results  are  more  nearly  in  accord  with  those  of  Plateau 
and  Forel,  there  is  sufficient  variation  in  them  with  respect  to  the  various 
species  of  flowers  and  insects,  as  indeed  there  is  in  those  of  these  two  investi- 
gators, to  make  it  unnecessary  to  question  the  observations  of  Andreae, 
Wery,  and  others.  It  has  been  repeatedly  demonstrated  that  insects  are  not 
repelled  by  paper  or  cloth  flowers  or  by  composite  imitations,  and  it  is  no 
longer  possible  to  uphold  Plateau's  contention  that  insects  do  not  go  to  arti- 
ficial blossoms  because  odor  is  more  powerful  than  color  in  attraction.  In  the 
major  number  of  investigations  they  have  been  found  to  visit  such  flowers 
abundantly  and  repeatedly,  and  to  prefer  them  all  but  exclusively  to  honey 
or  odor  alone,  as  Andreae  and  Wery  in  particular  have  shown. 

Painted  flowers. — While  painted  flowers  are  artificial  in  a  sense,  this 
is  true  to  a  much  smaller  degree  than  of  paper  or  cloth  ones,  as  is  shown 
by  the  relative  number  of  visits.     They  have  been  modified  as  to  color 


GENERAL  RESUME.  241 

primarily,  and  perhaps  slightly  as  to  surface  texture  and  odor.  Their 
greater  naturalness  is  attested  by  the  fact  that  they  received  about  five 
times  as  many  visitors  as  the  paper  composites  employed.  With  respect 
to  total  response  they  were  half  as  attractive  as  normal  blossoms,  though 
in  the  case  of  particular  species  they  were  equally  or  even  more  attractive. 
Thus,  painted  flowers  of  Rubus  deliciosus  were  visited  as  readily  as  normal 
ones,  and  in  the  installations  of  Aconitum  and  Chamaenerium  they  received 
a  larger  number  of  visits  absolutely.  The  greatest  number  of  visits  to  such 
flowers  was  made  by  Bombus  juxtus,  but  in  two  experiments  the  honey-bee 
made  twice  as  many  visits  to  them.  The  behavior  of  the  latter  was  espe- 
cially significant,  since  it  ignored  paper  flowers  altogether,  but  visited  about 
half  as  many  painted  as  normal  ones.  On  the  whole,  it  seems  clear  that 
changing  the  color  of  flowers  as  well  as  giving  a  wider  range  in  color  dis- 
turbed the  response  of  bees,  but  to  a  much  smaller  degree  than  artificial 
flowers  proper.  The  results  secured  by  painting  the  white  flowers  of  Rubus 
suggest  that  making  these  more  conspicuous  overcomes  the  disturbance 
arising  from  the  addition  of  the  water-colors,  and  indicate  that  white  flowers 
should  be  preferred  for  experiments  of  this  kind. 

Inclosing  flowers  in  glass. — Glass  containers,  such  as  beakers,  tubes,  and 
globes,  have  been  employed  by  several  investigators  to  eliminate  odor  and 
determine  the  response  to  color  alone.  Andreae  placed  flowers  under  bell- 
glasses  or  beneath  inverted  beakers  and  found  that  they  received  many  visits, 
in  spite  of  the  absence  of  odor.  Wery  also  found  out  that  cut  flowers  in  a  closed 
globe  exerted  nearly  normal  attraction.  The  conical  disk  of  three  heads 
of  Rudbeckia  was  covered  with  a  glass  tube  by  Detto,  with  the  consequence 
that  numerous  bees  flew  against  the  glass.  Allard  made  use  of  boxes  with 
a  glass  face  and  found  that  the  inspections  of  the  cotton  blossoms  were 
reduced  about  half.  These  experiments  show  conclusively  that  color  by 
itself  serves  to  attract  insects  in  quantity,  and  to  a  degree  equaling  or 
exceeding  that  of  odor.  This  is  confirmed  by  the  experiments  in  masking 
and  covering  discussed  in  the  next  section,  the  effect  being  to  eliminate 
color  and  to  render  odor  the  sole  attractive  force. 

Green  flowers  and  showy  nectarless  flowers. — Plateau  contended 
that  green  or  dull-colored  flowers  which  are  visited  by  insects  demonstrate 
that  color  is  unnecessary  and  hence  ineffective  in  attraction.  Andreae 
showed  that  the  color  of  inconspicuous  flowers  was  often  more  attractive 
than  either  odor  or  honey,  and  Lovell  has  proved  that  green  leaves  with 
honey  are  much  less  attractive  than  yellow  immortelles.  When  a  head  of 
golden  glow  and  a  green  spike  of  Amarantus  were  placed  in  competition, 
the  former  obtained  all  told  51  visits  to  16  for  the  latter.  Plateau  likewise 
insisted  that  the  failure  of  showy  nectarless  flowers  to  attract  insects  proved 
that  color  was  unimportant,  and  that  it  was  necessary  to  supply  them  with 
a  sweet  fragrant  liquid  to  induce  bees  to  come.  Perez  observed  that  bees 
did  go  to  showy  flowers  without  nectar,  but  that  they  soon  learned  the  futil- 
ity of  this  and  ignored  such  blossoms.  They  came  readily  to  geranium 
flowers  supplied  with  honey,  and  not  only  returned  to  them  after  the  honey 
was  exhausted,  but  also  went  to  others  that  had  received  no  honey.  Giltay 
found  that  bees  trained  to  come  to  geranium  flowers  with  honey  went  read- 


242  PRINCIPLES  AND  CONCLUSIONS. 

ily  to  flowers  without  it  when  these  occupied  the  same  place,  although 
they  were  unable  to  find  honeyed  leaves.  Lovell  noted  visits  to  showy 
nectarless  flowers  and  was  able  to  increase  these  by  the  addition  of  sugar 
sirup  with  odor,  thus  negativing  Plateau's  assumption.  In  the  case  of 
petunias,  honey-bees  continued  to  come  for  several  days  after  the  honey 
was  gone,  while  with  geranium  they  not  only  behaved  similarly,  but  also 
went  to  a  bed  of  Portulaca,  which  is  regularly  ignored,  and  inspected  the 
flowers  repeatedly. 

Thus,  it  is  evident  that  the  positive  response  to  dull  flowers  with  nectar 
and  the  negative  one  to  showy  nectarless  blossoms  are  largely  matters  of 
experience  and  habit,  in  the  case  of  adult  insects.  The  nectar  or  pollen 
reward  being  equal,  bright  flowers  are  visited  more  than  green  ones,  and, 
conversely,  the  size  and  color  being  equal  or  approximately  so,  flowers  are 
visited  in  proportion  to  the  amount  and  accessibility  of  their  nectar,  the 
nectarless  ones,  no  matter  how  showy,  receiving  no  visits  after  the  bees 
have  determined  the  absence  of  nectar.  Here,  as  elsewhere,  it  is  desirable 
to  work  with  flowers  of  each  sort  that  are  entirely  unknown  to  a  particular 
insect  community,  and  with  newly  hatched  bees,  which  are  necessarily 
without  experience. 

Color  preference. — The  view  that  bees  do  not  discriminate  between 
colors  has  been  advanced  by  Bonnier,  Bulman,  Plateau,  Forel,  MacLeod, 
and  others.  Bulman  stated  that  "it  matters  not  one  iota  to  a  bee  whether 
the  flower  is  blue,  red,  pink,  yellow,  white  or  green;  so  long  as  there  is  honey, 
that  is  sufficient,"  a  statement  approved  by  both  Plateau  and  Forel.  They 
have  failed  to  reckon  with  intelligence  and  habit,  however,  as  well  as  with 
the  fact  that  odor  and  form  doubtless  enable  the  bee  to  recognize  that  the 
difference  in  color  is  immaterial  to  him.  Darwin  appreciated  the  significance 
of  this  when  he  said,  "humble  and  hive  bees  are  good  botanists,  for  they 
know  that  varieties  may  differ  widely  in  the  color  of  their  flowers  and  yet 
belong  to  the  same  species"  (1876:416),  and  Lovell  in  particular  has  con- 
firmed the  view  of  Lubbock  and  Mueller  that  bees  easily  distinguish  colors 
and  go  to  some  in  preference  to  others.  Mueller  (1883:275)  pointed  out 
that  it  is  necessary  to  keep  in  mind  certain  characteristics  of  the  honey-bee 
in  connection  with  its  color  preferences,  if  one  is  to  avoid  hasty  conclu- 
sions. Chief  among  these  are  their  shyness  and  lack  of  cleverness  in  unac- 
customed surroundings.  However,  their  shyness  and  desire  for  freedom 
are  overruled  by  the  all-powerful  impulse  for  honey.  The  shyness  and  lack 
of  skill  of  bees  in  unaccustomed  places  are  in  marked  contrast  to  their  prompt 
decisions  and  shrewdness  at  flowers.  On  flowers  to  which  they  are  not 
especially  adapted,  various  individuals  often  behave  very  differently,  and 
they  also  show  great  individual  differences  in  their  color  preferences. 

Bonnier  decided  that  bees  exhibited  no  choice  between  red,  yellow, 
green  and  white,  but  his  results  were  regarded  as  inconclusive  by  Lubbock, 
since  his  squares  were  largely  covered  by  the  bees,  and  since  he  omitted  blue 
and  used  no  uncolored  checks.  Lubbock  made  most  extensive  experiments, 
which  disclosed  a  decided  choice  for  blue,  with  white  and  yellow  usually 
next.  To  avoid  artificial  colors,  Mueller  employed  detached  petals,  but 
obtained  similar  results.  While  there  were  marked  individual  differences, 
there   were  but  few   cases   in   which  one   or  more   individuals  reversed 


GENERAL  RESUME.  243 

the  preference  (p.  139).  The  least  attractive  of  all  colors  was  glaring 
yellow;  white  and  yellowish-white  were  visited  about  as  readily  as  many 
shades  of  purple,  but  less  readily  than  blue  or  violet.  Violet  excelled 
all  other  flower  colors  except  blue,  a  pure  deep  shade  of  the  latter  having 
the  advantage  indicated  by  the  ratios  81:37  and  50:35.  Among  the 
brilliant  flower  colors,  bright  yellow  was  the  most  attractive.  The  green 
of  leaves  was  less  than  half  as  attractive  as  rose,  but  slightly  more  so  than 
scarlet  or  orange.  Forel  found  that  Bombus  exhibited  a  distinct  preference 
for  blue  over  red,  though  he  appears  to  have  forgotten  the  inability  of  the  bee 
to  find  honey  on  red  or  to  have  felt  that  this  had  no  relation  to  the  behavior 
of  bees  at  flowers.  Plateau  showed  that  insects  made  no  choice  between  the 
differently  colored  flowers  of  the  same  species  or  variety,  but  entirely  over- 
looked habit  as  an  explanation  of  this.  He  did  prove,  however,  that  in 
his  experiments  at  least  the  so-called  admiration  of  syrphids  for  bright 
colors,  mottling,  etc.,  was  little  different  from  their  behavior  before  color- 
less or  inanimate  objects. 

Contrary  to  the  results  of  Lubbock  and  Forel  with  wasps,  the  Peckhams 
found  that  wasps  rely  very  greatly  upon  color  for  their  guidance,  a  change 
in  the  color  of  paper  about  the  nest  often  causing  all  of  them  to  hesitate 
or  go  to  the  misplaced  color.  This  is  in  harmony  with  the  instances  cited 
by  Theen,  Buttel-Reepen,  and  Lovell  of  the  effect  of  changing  the  color 
of  hives  or  their  thresholds.  Lovell  corroborated  the  preference  of  bees 
for  blue,  15  going  to  this  and  but  1  or  2  to  any  other  color.  A  bee  trained 
to  red  first  gave  a  ratio  of  8:2  for  red  and  blue,  but  finally  this  shifted  to 
3 : 7.  Turner  showed  that  as  a  rule  bees  did  not  visit  artefacts  of  the  color 
from  which  they  had  not  been  trained  to  forage  when  these  were  supplied 
with  honey  and  scattered  among  the  others.  Frisch  found  that  bees  paid 
no  attention  to  gray  in  competition  with  blue  or  yellow,  but  that  they  visited 
red,  dark  gray,  and  black  disks  indifferently.  He  concluded  that  bees  are 
color-blind  to  red  and  a  certain  shade  of  blue-green,  in  agreement  with  the 
views  of  Ladd-Franklin.  Since  there  are  many  records  of  visits  to  both 
these  colors,  which  must  have  appeared  in  varying  shades,  and  since  several 
shades  of  green  have  been  much  visited  in  the  course  of  the  present  inves- 
tigation, it  is  clear  that  further  experimentation  by  means  of  colors  of 
known  value  is  needed  in  this  field  (cf.  Frisch,  Knoll,  Kiihn  and  Pohl,  pp. 
200  to  207). 

While  the  different  colors  of  the  same  variety  or  species  may  have  no 
significance  for  insects,  it  is  evident  that  this  is  not  true  of  the  changes 
in  color  shown  by  flowers  in  maturing  or  withering.  Such  colors  are  helpful 
in  guiding  the  insect  and  saving  his  time,  and  he  regularly  takes  advantage  of 
them.  Mueller  (1883 :  81)  observed  that  in  a  field  of  red  and  blue  Pulmonaria 
females  of  Anthophora  pilipes  visited  almost  exclusively  the  red  blossoms 
and  those  just  beginning  to  change  toward  blue,  but  only  rarely  the  blue  ones. 
F.  Mueller  (1877: 17)  found  that  Lantana  flowers  were  visited  by  butterflies 
on  the  first  and  second  day  when  they  were  yellow  and  orange-red,  but 
never  on  the  third  when  they  were  purple;  some  species  in  fact  visited  the 
yellow  flowers  alone.  Here  the  perferences  were  naturally  not  for  the  colors 
as  such,  but  as  indicators  of  the  availability  of  nectar  (cf.  Ludwig,  1885, 
1887).     In   conclusion,  it    may  be  affirmed   that   trained   bees   exhibit   a 


244  PRINCIPLES  AND  CONCLUSIONS. 

marked  and  often  persistent  choice  for  the  proper  color,  but  that  there  is 
a  general  preference  for  blue.  In  field  and  garden,  differences  in  color  are  of 
great  importance  in  attraction,  but  the  bee  discriminates  among  them  only 
when  it  is  to  its  advantage  to  do  so,  as  between  species,  or  between  partly- 
open  buds  or  old  flowers  on  the  one  hand  and  fresh  ones  on  the  other.  When 
the  flowers  differ  in  color  alone,  the  bee  has  learned  that  this  is  unimportant 
in  comparison  with  odor  and  form.  When  a  new  factor  is  interjected,  how- 
ever, as  in  the  case  of  flowers  habitually  visited  which  are  changed  by 
painting  them  with  water-colors,  a  preference  is  manifested  until  experience 
again  shows  that  it  is  undesirable  or  unnecessary. 

ODOR. 

Masking  or  covering  flowers  to  conceal  color. — Plateau  thought  to 
have  demonstrated  by  masking  flowers  and  heads  with  paper  or  green  leaves 
that  color  is  of  little  or  no  value  in  attraction  and  that  odor  alone  is  suf- 
ficient. Most  of  his  experiments  lacked  checks  or  controls,  and  were  con- 
tradicted by  those  of  Forel,  who  found  that  flowers  completely  masked 
received  no  visits.  Wherever  a  slight  gap  permitted  entrance,  bees  soon 
found  their  way  in  and  then  returned  regularly  by  the  same  route.  More- 
over, after  the  lapse  of  several  hours  they  discovered  the  flowers  and  then 
visited  them  normally.  Andreae  frequently  employed  beakers  masked  with 
dark  paper  to  determine  the  effect  of  odor  alone;  in  three  representative 
cases  the  ratios  for  color  and  odor  were  10:0,  31:1,  and  35:3,  indicating 
that  odor  is  much  less  effective  than  color  as  a  rule.  Wery  noted  32  visitors 
to  normal  flowers  to  7  for  similar  ones  hidden  in  foliage,  and  19  to  artificial 
flowers  fully  exposed  to  but  4  for  those  concealed  in  leaves.  Giltay  repeatedly 
masked  flowers  with  pots  so  that  no  color  was  visible,  but  the  odor 
could  regularly  escape;  such  blossoms  received  no  visits,  but  bees  came 
readily  as  soon  as  the  pot  was  removed.  When  petals  were  placed  in  a  dish 
and  covered  with  a  pot  so  that  they  were  invisible  but  the  odor  could  escape 
they  were  never  visited,  but  after  the  pot  was  removed,  bees  alighted  on 
them,  sometimes  immediately.  Allard  concealed  a  cotton  blossom  so  that 
it  was  visible  only  from  above;  this  obtained  but  1  visit  to  12  for  the  control. 
When  the  disguise  was  taken  away,  the  flower  was  inspected  more  than  the 
control. 

These  experiments  leave  no  question  that  for  the  flowers  concerned 
at  least  the  role  of  color  in  attraction  is  usually  several  times  and  often 
many  times  greater  than  that  of  odor. 

Odor  of  honey. — While  honey  has  a  strong  attractive  power,  this  is  due 
chiefly  to  its  sweetness  and  but  little  to  its  odor,  especially  in  the  case  of  bees. 
Even  Plateau  had  remarked  the  fact  that  bees  have  a  weak  sense  of  smell 
for  honey,  and  this  inability  has  been  emphasized  by  Forel,  Buttel-Reepen, 
Giltay,  Wery,  Detto,  Lovell,  and  others.  Bombus  and  Apis  have  repeatedly 
been  observed  to  pass  within  a  few  millimeters  of  honey  in  both  natural  and 
artificial  flowers  without  perceiving  it.  In  some  cases  they  have  even 
become  entangled  in  it  and  tried  to  clean  it  off  without  recognizing  it. 
Moreover,  sugar  sirups  and  other  sweet  liquids  without  odor  have  often  been 
found  to  be  quite  as  attractive  as  honey.  Once  found,  honey  is  a  powerful 
incentive  to  return  until  it  is  exhausted.     In  our  experiments  it  never  in- 


GENERAL  RESUME.  245 

creased  the  number  of  visits  to  natural  flowers  and  had  practically  no  effect 
upon  those  to  artificial  ones.  In  the  majority  of  cases  it  actually  decreased 
the  number  of  visits,  often  as  much  as  ten  times.  Wery  found  that  honey 
remained  practically  untouched  in  competition  with  natural  or  artificial 
flowers,  obtaining  such  ratios  as  49:0  and  25:0,  and  emphasized  the  fact 
that  honey  attracts  bees  very  little. 

Effect  of  added  odors. — In  his  first  studies  of  the  effect  of  adding  odors 
to  flowers  Plateau  obtained  no  conclusive  results.  Thyme  and  sage  appeared 
to  attract  feebly,  lavender  not  at  all,  and  mint  to  repel.  In  his  later  studies, 
he  stated  that  it  was  indispensable  for  good  results  to  avoid  essences  and 
to  employ  substances  known  to  attract.  With  these  he  had  marked  success 
with  but  one  or  two,  such  as  anisette,  a  sugar  sirup  flavored  with  anise. 
On  the  other  hand,  our  experiments  showed  a  decrease  of  50  per  cent  in 
the  number  of  visits  when  various  perfumes  and  essences  were  added,  even 
in  the  presence  of  honey.  With  occasional  exceptions,  perfumes  in  them- 
selves have  no  effect  in  increasing  attraction,  though  they  may  serve  as 
indicators  of  the  presence  of  honey  or  sirup  and  thus  seem  to  be  attractive, 
as  in  Plateau's  results.  It  is  possible  that  positive  results  would  be  secured 
by  using  perfume  from  flowers  that  bees  had  been  visiting  in  other  areas  or 
earlier  in  the  season,  and  such  experiments  are  now  under  way. 

Relative  value  of  color  and  odor. — Wery  has  endeavored  to  give 
quantitative  expression  to  the  respective  parts  played  by  color,  form,  odor, 
and  food  in  the  attraction  of  insects,  and  her  values  seem  to  be  fair  approx- 
imations of  the  various  roles.  Her  general  conclusion  in  this  respect  was 
formulated  as  follows : 

"For  the  honey-bee  the  attraction  exerted  by  the  form  and  color  of  flowers  is  ap- 
proximately four  times  greater  than  that  of  their  pollen,  perfume,  and  nectar  taken 
together.  Thus,  if  the  total  attraction  exerted  by  the  most  attractive  flowers  is  taken 
as  100,  that  of  form  and  color  will  be  represented  by  about  80  and  that  of  the  other 
three  factors  by  about  20." 

In  view  of  the  faint  sense  of  smell  for  honey  and  pollen  exhibited  by  bees, 
this  seems  a  conservative  figure  except  for  flowers  with  a  marked  perfume, 
which  are  still  to  be  adequately  investigated.  It  is  these  flowers  that  have 
given  rise  to  contradictory  opinions  as  to  the  relative  share  of  color  and  odor 
in  attraction  from  a  distance  and  guidance  near  at  hand. 

FORM. 
Distinction  and  role. — Following  the  views  of  Exner  as  to  vision,  both 
Plateau  and  Forel  were  of  the  opinion  that  insects  distinguish  forms  more 
or  less  vaguely,  except  when  in  motion.  When  one  recalls  the  incessant 
activity  of  bees  on  flowers,  this  exception  is  nearly  tantamount  to  the 
admission  that  insects  do  distinguish  forms  and  make  use  of  them  in  deter- 
mining their  visits.  Although  Perez  regarded  form  as  less  important  than 
color  or  odor,  he  pointed  out  the  contradiction  involved  in  Plateau's  con- 
tention that  insects  could  not  distinguish  colors,  but  that  they  were  guided 
to  buds,  withered  flowers,  and  fruits  by  their  form.  Moreover,  Forel  stated 
that  wasps  readily  recognize  the  forms  and  contours  of  objects,  and  he 
demonstrated  that  wasps  and  bumble-bees  could  distinguish  bands  from 


246  PRINCIPLES  AND   CONCLUSIONS. 

disks.  He  also  declared  that  his  experiments  with  artefacts  demonstrated 
that  honey-bees  possess  the  perception  of  space,  form,  and  color.  Practi- 
cally all  other  students  of  experimental  pollination  have  agreed  that  insects 
are  guided  in  some  degree  by  form,  though  Giltay  thought  that  visits  to 
a  single  petal  indicated  that  form  could  not  be  concerned.  This  does  not 
follow,  however,  since  it  is  evident  that  color  is  often  more  potent  than 
form.  Detto  was  also  doubtful  of  the  ability  of  bees  to  see  forms,  but  he 
explains  certain  of  his  results  on  the  assumption  that  the  bees  were  able  to 
recognize  the  stamens  and  pistil  of  a  flower.  The  Peckhams,  Dahl,  Andreae, 
Wery,  Frisch,  and  Turner  have  shown  that  insects  distinguish  forms  or 
patterns,  and  some  of  Lovell  and  Allard's  results  permit  no  other  conclusion. 
Additional  proof  is  furnished  by  the  readiness  with  which  they  go  from  one 
color  to  another  of  flowers  of  the  same  species  or  variety,  whether  fragrant 
or  not,  and  especially  by  their  response  to  painted  flowers.  The  minuteness 
with  which  they  can  distinguish  forms  and  structures  is  proved  by  the  ease 
with  which  they  solve  the  problems  presented  by  inverted  and  mutilated 
flowers,  as  well  as  by  the  ingenious  experiments  of  Detto  on  the  relative 
importance  of  vision  and  smell  in  enabling  insects  to  locate  the  nectary  open- 
ings. Finally,  it  appears  that  insects  can  distinguish  differences  in  surface 
and  texture  sufficiently  small  to  escape  man.  This  conclusion  seems  un- 
avoidable, when  one  recalls  the  readiness  with  which  bees  often  distinguish 
between  the  best  of  artificial  or  painted  flowers  and  normal  ones.  In  fact, 
it  is  a  curious  paradox  that  Plateau,  who  thought  insects  distinguish  neither 
form  nor  color,  and  that  Forel,  who  thought  they  had  but  a  vague  vision 
of  form,  should  have  believed  that  they  were  able  to  discriminate  between 
artificial  and  natural  flowers  by  means  of  other  differences  not  visible  to 
the  eyes  of  man. 

ATTRACTION  AT  A  DISTANCE  AND  NEAR  AT  HAND. 

It  is  unfortunate  that  no  definite  experiments  have  been  made  as  to  the 
distance  at  which  various  colors  and  odors  as  represented  in  flowers  exert 
attraction,  but  it  is  hoped  that  the  experiments  now  contemplated  will 
yield  accurate  quantitative  results.  The  general  opinion  has  been  that 
odor  attracts  from  a  distance  and  color  near  at  hand,  and  Plateau  has  defi- 
nitely stated  that  insects  do  not  perceive  objects  at  a  greater  distance  than 
2  meters  and  many  of  them  only  when  much  nearer.  On  the  other  hand, 
Wery  believed  that  color  could  attract  for  a  distance  of  6  meters,  since 
insects  were  able  to  recognize  artificial  blossoms  placed  this  far  from  natural 
ones,  and  Andreae  stated  that  honey-bees  could  see  8  to  10  meters  at  least, 
basing  this  upon  similar  grounds. 

The  careful  consideration  of  previous  experiments  confirms  the  evidence 
derived  from  the  present  investigation.  This  indicates  as  the  best  working 
hypothesis  for  further  studies  the  conclusion  that  odor  attracts  for  distances 
beyond  10  meters,  color  in  mass  for  the  intermediate  ones,  and  color  and 
form  in  detail  within  a  meter  or  so,  depending  greatly  upon  the  size  and 
color  of  the  flower  or  cluster.  For  the  majority  of  flowers  without  a  marked 
fragrance,  odor  can  be  effective  only  when  near  at  hand  and  the  effect  is 
probably  small  even  then.  It  is  hardly  necessary  to  point  out  that  this 
must  be  true  of  color  also  in  the  case  of  green  or  dull  flowers  and  especially 


GENERAL  RESUME.  247 

those  of  small  size.  Since  the  senses  of  sight  and  smell  differ  greatly  in  the 
various  groups  of  insects,  the  relative  importance  of  the  three  attractive 
factors  will  be  modified  accordingly.  In  a  group  of  plants  or  a  floriferous 
individual  or  even  in  the  midst  of  a  cluster  of  flowers,  odor  can  have  little 
effect,  except  in  the  rare  instances  when  very  fragrant  flowers  or  clusters 
are  widely  separated  in  such  groups.  The  odor  is  not  only  general,  but  it 
is  naturally  most  powerful  at  the  flower  or  cluster  on  which  the  insect  is 
working.  Such  conditions  would  not  permit  it  to  go  straightway  and  with- 
out an  instant's  hesitation  to  the  next  flower  or  head,  and  guidance  by 
color  and  form  alone  can  explain  the  assured  and  rapid  flight  of  bees  in  the 
midst  of  flowers.  This  is  confirmed  by  their  behavior  when  the  wind  is 
blowing,  for  they  fly  most  easily  with  the  wind,  though  this  carries  the 
fragrance  of  the  next  flower  sought  away  from  them.  Moreover,  the  readi- 
ness with  which  they  often  drop  from  the  midst  of  a  plant  or  bush  to  fallen 
corollas  on  the  ground  a  foot  or  more  below  further  supports  the  view  that 
odor  is  rarely  a  guide  among  flowers.  However,  it  must  be  kept  in  mind 
that  such  studies  have  so  far  been  incidental  and  concerned  with  bees  al- 
ready habituated  to  the  flowers  concerned,  except  in  some  of  the  competi- 
tion studies  already  given  in  chapter  3. 

LEARNING  AND  HABIT. 

It  is  possible  at  present  to  deal  with  learning  and  habit  only  in 
the  general  qualitative  manner  so  admirably  exemplified  in  the  work 
of  Lubbock,  Mueller,  Forel,  Peckham,  Buttel-Reepen,  Detto,  Lovell,  Turner, 
Frisch,  and  Knoll.  The  time  has  come  for  a  comprehensive  quantitative 
attack  on  the  learning  process  and  its  relation  to  the  fixation  and  modi- 
fication of  habit,  and  one  of  the  primary  objects  of  the  present  book  is 
to  clear  the  way  for  such  investigation,  as  indicated  earlier.  In  view  of 
their  generalized  mental  organization,  the  ability  of  insects,  and  especially 
the  bees,  to  learn  by  experience  is  remarkable.  This  has  been  widely  recog- 
nized by  experimenters  in  this  field,  though  it  has  been  doubted  by  some 
who  failed  to  take  into  account  the  qualities  emphasized  by  Mueller, 
namely,  the  shyness  and  lack  of  cleverness  in  unusual  surroundings  and  the 
all-powerful  obsession  for  honey.  The  ease  and  rapidity  with  which  habits 
of  landing  and  securing  nectar  are  modified  under  changed  conditions 
indicate  a  great  power  of  learning  and  a  corresponding  plasticity  of 
habit  that  is  surprising.  These  qualities  will  probably  be  found  to  be 
even  more  marked  in  the  case  of  newly  hatched  or  young  insects,  and  it  is 
possible  that  the  training  of  these  will  disclose  new  possibilities  of  learn- 
ing and  adjustment.  As  the  work  of  Giltay  shows,  the  selection  of  marked 
individuals  on  the  basis  of  different  types  of  response  opens  a  new  vista 
in  this  field,  and  permits  the  extension  and  refinement  of  our  knowledge 
of  the  mental  powers  of  the  species  and  group  by  means  of  the  psychology 
of  the  individual. 

MEMORY  AND   INTELLIGENCE. 

The  Peckhams  concluded  that  wasps  have  a  very  good  memory,  and 
Forel  stated  that  bees  not  only  have  memory  for  place  but  also  for  time, 
a  statement  in  accord  with  the  views  of  Buttel-Reepen.      Probably  the 


248  PRINCIPLES  AND   CONCLUSIONS. 

most  remarkable  instance  of  memory  is  that  recorded  by  Hoffer  (1886:11), 
who  found  that  bumble-bees  remembered  the  place  in  which  their  nest 
had  been  put,  from  the  middle  of  October  when  they  disappeared  to  the 
beginning  of  April  when  they  returned.  It  is  evident  also  that  wasps 
in  particular  have  a  remarkable  memory  for  forms  and  outlines  along 
the  path  of  their  flights,  as  shown  by  their  ability  to  find  their  way  back 
for  several  miles,  a  faculty  only  less  developed  in  the  bees. 

Both  Buttel-Reepen  and  Forel  have  shown  that  bees  are  capable  of 
memory  and  other  associations,  and  the  former  stated: 

"We  see  that  bees  show  signs  of  an  admirable  memory  in  their  orientation  and  in 
their  other  activities;  further,  I  believe  I  have  shown  that  the  bee  possesses  a  perception 
for  color  and  form,  and  develops  a  rich  capacity  for  communication  by  means  of  its 
well-developed  'language';  that,  further,  it  is  able  to  gather  experiences,  to  learn 
and  to  form  associations  of  impressions,  etc." 

Forel  independently  declared  that — 

"It  ensues  from  the  concordant  observations  of  all  the  experts  that  sensation, 
perception,  association,  inference,  memory,  and  habit  in  the  social  insects  follow  the 
same  fundamental  laws  as  in  the  vertebrates  and  ourselves.  In  these  animals  it  is 
possible  to  demonstrate  the  existence  of  memory,  associations  of  sensory  images, 
perception,  attention,  habits,  simple  powers  of  inference  from  analogy,  the  utilization 
of  individual  experiences  and  hence  distinct,  though  feeble,  plastic  individual  de- 
liberations or  adaptations.  It  is  also  possible  to  detect  a  corresponding,  simpler  form 
of  volition,  i.  e.,  the  carrying  out  of  individual  decisions  in  a  more  or  less  protracted 
time  sequence,  through  different  concatenations  of  instincts;  furthermore,  different 
kinds  of  discomfort  and  pleasure  emotions,  as  well  as  interactions  and  antagonisms 
between  these  diverse  psychic  powers." 

As  early  as  1877,  Forel  said  that  all  the  properties  of  the  human  mind 
may  be  derived  from  the  properties  of  the  animal  mind  and  a  quarter  of 
a  century  later  he  merely  added  the  statement  that  all  the  mental  attributes 
of  higher  animals  may  be  derived  from  those  of  lower  animals. 

With  the  development  of  more  exact  methods  in  comparative  psychology 
has  gone  a  more  critical  spirit,  which  has  discarded  practically  all  the 
observational  and  anecdotal  material  so  long  utilized.  The  same  feeling 
for  accuracy  and  objectivity  has  led  to  the  present  endeavor  to  place  the 
study  of  the  relations  of  flowers  and  insects  upon  a  purely  experimental 
basis.  In  spite  of  this,  however,  the  work  of  Forel,  Lubbock,  the  Peckhams, 
Buttel-Reepen,  Ferton,  and  others  was  so  largely  experimental  that  their 
general  conclusions  have  remained  true  and  still  constitute  much  of  the 
essential  foundation  for  the  study  of  insect  psychology,  as  is  evident  from 
the  recent  and  more  exact  researches  of  Frisch,  Knoll,  and  Kuhn  and  Pohl 
[see  also  Holmes  (1911),  Thorndike  (1911),  Smith  (1915),  and  Bouvier 
(1922)]. 


5.  POLLINATORS  AND  FLOWERS  VISITED. 


Acmaeops  longicornis : 

Carduus  hookerianus. 

Mertensia  sibirica. 

Prunus  demissa. 

Rosa  acicularis. 

Rubus  deliciosus. 
Acmaeops  pratensis: 

Prunus  demissa. 

Rosa  acicularis. 

Rubus  deliciosus. 
Agapostemon  color adensis: 

Stanleya  pinnatifida. 

Taraxacum  officinale. 
Agapostemon  splendens: 

Malvastrum  coccineum. 

Pentstemon  glaber. 

Rosa  acicularis. 

Taraxacum  officinale. 
Agapostemon  sp.: 

Prunus  demissa. 

Stanleya  pinnatifida. 
Agathis  vulgaris: 

Achillea  millefolium. 
Ancistrocerus  sp. : 

Geranium  caespitosum. 
richardsoni. 

Jamesia  americana. 

Mertensia  sibirica. 

Rubus  deliciosus. 
strigosus. 
Andrena  apacheorum: 

Erigeron  macranthus. 

Geranium  caespitosum. 
Andrena  braccata: 

Geranium  caespitosum. 
Andrena  canadensis: 

Prunus  demissa. 

Rubus  deliciosus. 
Andrena  crataegi: 

Carduus  hookerianus. 

Frasera  speciosa. 

Holodiscus  dumosus. 

Monarda  fistulosa. 

Opulaster  opulifolius. 

Prunus  demissa. 

virginiana. 

Rosa  acicularis. 

Rubus  deliciosus. 
strigosus. 
Andrena  edwiniae: 

Jamesia  americana. 

Prunus  demissa. 
Andrena  gardineri: 

Astragalus  drummondi. 
Andrena  imitatrix: 

Astragalus  drummondi. 
Andrena  lewisi : 

Rubus  strigosus. 
Andrena  madronitens: 

Frasera  speciosa. 

Geranium  caespitosum. 
richardsoni. 

Holodiscus  dumosus. 


Andrena  madronitens — Con. 

Mertensia  sibirica. 

Onagra  biennis. 

Opulaster  opulifolius. 

Pentstemon  glaber. 

secundiflorus. 

Prunus  demissa. 

Rosa  acicularis. 

Rubus  deliciosus. 
strigosus. 

Sedum  stenopetalum. 
Andrena  placida: 

Rubus  deliciosus. 
Andrena  prunorum: 

Pentstemon  glaber. 

Prunus  demissa. 

virginiana. 

Rubus  deliciosus. 
Andrena  vicina: 

Astragalus  drummondi. 

Geranium  caespitosum. 

Pentstemon  glaber. 

Potentilla  arguta. 

Prunus  demissa. 

virginiana. 

Rosa  acicularis. 

Rubus  deliciosus. 
strigosus. 

Stanleya  pinnatifida. 
Andrena  washingtoni : 

Pentstemon  gracilis. 

Rosa  acicularis. 
Andrena  sp. : 

Prunus  demissa. 

virginiana. 

Rosa  acicularis. 
Andronicus  sp. : 

Carduus  hookerianus. 

Geranium  caespitosum. 

Pentstemon  gracilis. 

Rubus  deliciosus. 
Anthidium  tenuiflorae: 

Sedum  stenopetalum. 
Anthophora  bomboides: 

Pentstemon  glaber. 
Anthophora  occidentalis : 

Chamaenerium  angusti- 
folium. 
Anthophora  neomexicana: 

Pentstemon  gracilis. 
Anthophora  simillima: 

Aragalus  lamberti. 

Capnoides  aureum. 

Dodocatheon  meadia. 

Lithospermum  canescens. 

Pentstemon  glaber. 
gracilis, 
halli. 

secundiflorus. 
unilateralis. 

Rosa  acicularis. 

Rubus  strigosus. 

249 


Anthophora  smithi : 

Campanula  rotundifolia. 

Chamaenerium  angusti- 
folium. 

Monarda  fistulosa. 
Anthrax  alternata: 

Holodiscus  dumosus. 
Anthrax  fulviana: 

Erigeron  macranthus. 
Anthrax  halcyon: 

Solidago  missouriensis. 
Anthrax  hypomelas: 

Heracleum  lanatum. 

Potentilla  gracilis. 
Anthrax  lateralis: 

Rosa  acicularis. 
Anthrax  nigra: 

Rosa  acicularis. 
Anthrax  sinuosa: 

Sedum  stenopetalum. 

Tradescantia  virginiana. 
Anthrax  tegminipennis: 

Erigeron  macranthus. 
Anthomyia  sp. : 

Clementsia  rhodantha. 
Apanteles  sp. : 

Geranium  caespitosum. 
Apis  mellifica: 

Arctostaphylus  uva-ursi. 

Asclepias  halli. 

speciosa. 

Chamaenerium  angusti- 
folium. 

Frasera  speciosa. 

Geranium  caespitosum. 
richardsoni. 

Holodiscus  dumosus. 

Jamesia  americana. 

Linaria  vulgaris. 

Mentzelia  multiflora. 

Opulaster  opulifolius. 

Pentstemon  glaber. 

unilateralis. 

Petalostemon  candidus. 
purpureus. 

Rosa  acicularis. 

Rubus  deliciosus. 
strigosus. 

Solidago  missouriensis. 

Stanleya  pinnatifida. 

Taraxacum  officinale. 

Thalictrum  fendleri. 

Tradescantia  virginiana. 
Archytas  sp.: 

Geum  rivale. 
Arctophila  flagrans: 

Rosa  acicularis. 
Argynnis  atlantis: 

Chamaenerium  angusti- 
folium. 

Erigeron  macranthus. 

Monarda  fistulosa. 

Pentstemon  secundiflorus. 


250 


EXPERIMENTAL  POLLINATION. 


Argynnis  eurynome: 

Geranium  caespitosum. 

Helianthus  petiolaris. 
Rydbergia  grandiflora. 

Sedum  stenopetalum. 
Atrytone  taxiles: 

Capnoides  aureum. 

Chamaenerium  angusti- 
folium. 

Monarda  fistulosa. 

Pentstemon  glaber. 
Basilarchia  weidemeyeri: 

Linaria  vulgaris. 
Bembex  spinolae: 

Asclepias  halli. 
Bombomelecta  fulvida: 

Capnoides  aureum. 

Mertensia  sibirica. 

Pentstemon  glaber. 

gracilis. 

Bombus  americanorum: 

Pentstemon  unilateralis. 

Rubus  deliciosus. 

Thermopsis  montana. 
Bombus  appositus: 

Aconitum  columbianum. 

Carduus  hookerianus. 

Chamaenerium  angusti- 
folium. 

Delphinium  occidentale. 

Gentiana  parryi. 

Geranium  caespitosum. 

Ibidium  strictum. 

Monarda  fistulosa. 

Pentstemon  glaber. 
gracilis. 

Petalostemon  candidus. 
purpureus. 

Rubus  deliciosus. 

Rydbergia  grandiflora. 

Rosa  acicularis. 
Bombus  bifarius: 

Aconitum  columbianum. 

Carduus  hookerianus. 

Chamaenerium  angusti- 
folium. 

Delphinium  scopulorum. 

Dodocatheon  meadia. 

Elephantella  groenlandica. 

Erigeron  macranthus. 

Geranium  caespitosum. 
richardsoni. 

Holodiscus  dumosus. 

Jamesia  americana. 

Mentzelia  multiflora. 

Mertensia  sibirica. 

Monarda  fistulosa. 

Pentstemon  glaber. 
glaucus. 
gracilis, 
secundiflorus. 

Rosa  acicularis. 

Rubus  deliciosus. 
strigosus. 

Stanleya  pinnatifida. 


Bombus  centralis: 

Chamaenerium  angusti- 
folium. 

Delphinium  scopulorum. 

Monarda  fistulosa. 

Pentstemon  glaber. 
gracilis. 
Bombus  dorsalis: 

Capnoides  aureum. 
Bombus  edwardsi: 

Aconitum  columbianum. 

Allium  recurvatum. 

Arctostaphylus  uva  ursi. 

Aster  foliaceus. 

Astragalus  drummondi. 

Calochortus  gunnisoni. 

Campanula  rotundifolia. 

Carduus  hookerianus. 

Chamaenerium  angusti- 
folium. 

Chrysopsis  villosa. 

Cleome  serrulata. 

Delphinium  scopulorum. 

Dodocatheon  meadia. 

Drymocallis  fissa. 

Erigeron  macranthus. 

Fragaria  vesca. 

Frasera  speciosa. 

Geranium  caespitosum. 

Holodiscus  dumosus. 

Jamesia  americana. 

Lathyrus  ornatus. 

Mertensia  sibirica. 

Opulaster  opulifolius. 

Pedicularis  racemosa. 

Pentstemon  glaber. 
glaucus. 
gracilis, 
secundiflorus. 

Petalostemon  candidus. 
purpureus. 

Rosa  acicularis. 

Rubus  deliciosus. 
strigosus. 

Rydbergia  grandiflora. 

Sedum  stenopetalum. 

Sieversia  ciliata. 

Solidago  missouriensia. 
Bombus  fervidus: 

Astragalus  drummondi. 

Monarda  fistulosa. 

Pentstemon  unilateralis. 

Petalostemon  candidus. 
purpureus. 

Rubus  deliciosus. 
Bombus  flavifrons: 

Aconitum  columbianum. 

Aster  foliaceus. 

Calochortus  gunnisoni. 

Chamaenerium  angusti- 
folium. 

Dasyphora  fruticosa. 

Delphinium  scopulorum. 

Dodocatheon  meadia. 


speciosa. 
Mertensia  sibirica. 
Monarda  fistulosa. 


Bombus  flavifrons — Con. 
Prunus  demissa. 
Rosa  acicularis. 
Rubus  deliciosus. 
strigosus. 
Rydbergia  grandiflora. 
Solidago  missouriensis. 
Bombus  fulvida: 

Mertensia  sibirica. 
Bombus  hunti: 

Aquilegia  brevistyla. 

coerulea. 
Astragalus  drummondi. 
Campanula  rotundifolia. 
Carduus  hookerianus. 
Castilleia  miniata. 
Chamaenerium  angusti- 

folium. 
Erigeron  macranthus. 

uniflorus. 
Frasera  speciosa. 
Geranium  caespitosum. 
richardsoni. 
Helianthus  petiolaris. 
Holodiscus  dumosus. 
Jamesia  americana. 
Monarda  fistulosa. 
Pedicularis  parryi. 
Pentstemon  glaber. 

gracilis. 
Petalostemon  candidus. 

purpureus. 
Potentilla  gracilis. 
Rosa  acicularis. 
Rubus  deliciosus. 
strigosus. 
Rydbergia  grandiflora. 
Sedum  stenopetalum. 
Solidago  missouriensis. 
Stanleya  pinnatifida. 
Thermopsis  montana. 
Trifolium  dasyphyllum. 
Bombus  juxtus: 

Aconitum  columbianum. 
Astragalus  drummondi. 
Campanula  rotundifolia. 
Capnoides  aureum. 
Carduus  hookerianus. 
Chamaenerium  angusti- 

folium. 
Chrysopsis  villosa. 
Delphinium  scopulorum. 
Frasera  speciosa. 
Gentiana  parryi. 
Geranium  caespitosum. 
Holodiscus  dumosus. 
Jamesia  americana. 
Mentzelia  multiflora. 
Mertensia  sibirica. 
Monarda  fistulosa. 
Onagra  biennis. 
Pentstemon  glaber. 

glaucus. 

gracilis. 

secundiflorus. 

unilateralis. 
Potentilla  arguta. 


POLLINATORS   AND   FLOWERS. 


251 


Bombus  juxtus — Con. 

Rosa  acicularis. 

Rubus  deliciosus. 
strigosus. 

Thermopsis  montana. 
Bombua  kirbyellus: 

Castilleia  miniata. 

Pedicularis  parryi. 

Pentstemon  glaber. 

Potentilla  arguta. 

pulcherrima. 

Rubus  deliciosus. 

Trifolium  dasyphyllum. 
Bombus  morrisoni: 

Astragalus  drummondi. 

Delphinium  scopulorum. 

Ibidium  strictum. 

Monarda  fistulosa. 

Pentstemon  glaber. 
glaucus. 
gracilis. 

Rosa  acicularis. 

Rubus  deliciosus. 
strigosus. 

Scutellaria  resinosa. 

Stanleya  pinnatifida. 
Bombus  nevadensis : 

Carduus  hookerianus. 

Chamaenerium  angusti- 
folium. 

Gentiana  parryi. 

Opulaster  opulifolius. 
Bombus  occiden talis: 

Aconitum  columbianum. 

Allium  recurvatum. 

Aquilegia  coerulea. 

Calochortus  gunnisoni. 

Capnoides  aureum. 

Carduus  hookerianus. 

Castilleia  miniata. 

Chamaenerium  angusti- 
folium. 

Delphinium  scopulorum. 

Erysimum  asperum. 

Erigeron  uniflorus. 

Geranium  caespitosum. 
richardsoni. 

Heracleum  lanatum. 

Holodiscus  dumosus. 

Jamesia  americana. 

Linaria  vulgaris. 

Mentzelia  multiflora. 

Mertensia  sibirica. 

Monarda  fistulosa. 

Opulaster  opulifolius. 

Pedicularis  racemosa. 

Pentstemon  glaber. 
glaucus. 
secundiflorus. 

Petalostemon  purpureus. 

Potentilla  pulcherrima. 

Prunus  demissa. 

Rosa  acicularis. 

Rubus  deliciosus. 
strigosus. 

Sieversia  ciliata. 

Solidago  missouriensis. 


Bombus  pennsylvanicus: 

Monarda  fistulosa. 
Bombus  ruf ocinctus : 

Aconitum  columbianum. 

Calochortus  gunnisoni. 

Chamaenerium  angusti- 
folium. 

Geranium  caespitosum. 

Pentstemon  glaber. 
gracilis. 

Petalostemon  candidus. 
purpureus. 

Rosa  acicularis. 

Rubus  deliciosus. 

Solidago  missouriensis. 

Stanleya  pinnatifida. 
Bombylius  atriceps: 

Rosa  acicularis. 
Brachyopa  notata: 

Prunus  demissa. 

Rubus  deliciosus. 
Bracon  helena: 

Erigeron  macranthus. 
Bracon  vulgaris: 

Stanleya  pinnatifida. 
Brenthis  triclaris: 

Dasyphora  fruticosa. 

Prunus  demissa. 
Calliphora  vomitoria : 

Prunus  demissa. 
Celerio  lineata: 

Pachylophus  caespitosus. 

Pentstemon  glaber. 
Cenis  uhleri: 

Geranium  caespitosum. 
Cerastomia  lignaria: 

Pentstemon  gracilis. 
Ceratina  sp. : 

Mertensia  sibirica. 

Pentstemon  gracilis. 

Stanleya  pinnatifida. 
Chilosia  petulca: 

Prunus  demissa. 
Chilosia  tristis: 

Prunus  demissa. 
Chionobis  macouni: 

Draba  aurea. 

Iris  missouriensis. 

Potentilla  pulcherrima. 
Chrysogaster  parva: 

Rubus  deliciosus. 
Chrysophanus  helloides: 

Achillea  millefolium. 

Erigeron  macranthus. 

Oreochrysum  parryi. 
Chrysophanus  rubidus. 

Campanula  rotundifolia. 

Carduus  hookerianus. 

Phacelia  heterophylla. 
Chrysophanus  sirius: 

Monarda  fistulosa. 
Chrysotoxum  integrum: 

Holodiscus  dumosus. 

Rosa  acicularis. 
Chrysotoxum  upsilon: 

Polygonum  bistorts. 


Chrysotoxum  ventricosum : 

Potentilla  pulcherrima. 
Clisodon  terminalis: 

Aquilegia  coerulea. 

Carduus  hookerianus. 

Chamaenerium  angusti- 
folium. 

Frasera  speciosa. 

Geranium  caespitosum. 

Holodiscus  dumosus. 

Mertensia  pratensis. 

Monarda  fistulosa. 

Pentstemon  glaber. 
glaucus. 
gracilis, 
secundiflorus. 

Petalostemon  purpureus. 

Rosa  acicularis. 

Rubus  strigosus. 
Clisodon  sp.: 

Carduus  hookerianus. 

Mertensia  sibirica. 

Pentstemon  glaber. 
gracilis. 
Coelioxys  moesta: 

Chamaenerium  angusti- 
folium. 

Geranium  caespitosum. 
Coenonympha  pamphiloides : 

Dasyphora  fruticosa. 

Erigeron  macranthus. 

Prunus  demissa. 
Colias  alexandra: 

Potentilla  pulcherrima. 
Colias  edwardsi: 

Carduus  hookerianus. 
Colias  keewaydina: 

Castilleia  miniata. 
Colias  scudderi: 

Carduus  hookerianus. 
Colletes  americanus: 

Rosa  acicularis. 

Solidago  missouriensis. 
Colletes  kincaidi: 

Geranium  caespitosum. 

Pentstemon  gracilis. 

Petalostemon  purpureus. 

Prunus  demissa. 
Colletes  oromontis: 

Capnoides  aureum. 

Geranium  caespitosum. 

Holodiscus  dumosus. 

Mertensia  pratensis. 
sibirica. 

Monarda  fistulosa. 

Rubus  deliciosus. 
strigosus. 

Solidago  missouriensis. 
Colletes  sieverti: 

Geranium  caespitosum. 
Ctenucha  sp.: 

Chamaenerium  angusti- 
folium. 

Monarda  fistulosa. 
Curtipogon  leucozona: 

Calochortus  gunnisoni. 


252 


EXPERIMENTAL  POLLINATION. 


Dasyllis  fernaldi: 

Calochortus  gunnisoni. 
Chamaenerium  angusti- 
folium. 
Dejeania  vexatrix: 

Chamaenerium  angusti- 

folium. 
Mertensia  sibirica. 
Opulaster  opulifolius. 
Dolichovespula  arctica: 

Chamaenerium  angusti- 

fohum. 
Delphinium  scopulorum. 
Dolichovespula  diabolica: 
Chamaenerium  angusti- 
folium. 
Echinomyia  algens: 

Chamaenerium  angusti- 

folium. 
Chrysopsis  villosa. 
Heracleum  lanatum. 
Echinomyia  decias: 

Asclepias  speciosa. 
Ectemius  montanus: 

Geranium  richardsoni. 
Ectemius  muricatus: 

Heracleum  lanatum. 
Eliphilus  latifrons: 

Cleome  serrulata. 
Epalpus  bicolor: 

Carduus  hookerianus. 
Polygonum  bistorta. 
Solidago  missouriensis. 
Epalpus  rufus: 

Carduus  hookerianus. 
Valeriana  edulis. 
Epeolus  helianthi: 

Geranium  caespitosum. 
Erebia  epipsodea: 

Dasyphora  fruticosa. 
Geranium  caespitosum. 
Potentilla  pulcherrima. 
Prunus  demissa. 
Eristalis  arbustorum: 
Prunus  demissa. 
Rubus  strigosus. 
Eristalis  dimidiatus: 
Prunus  demissa. 
Eristalis  flavipes: 

Rubus  deliciosus. 
Eristalis  latifrons: 

Opulaster  opulifolius. 
Rosa  acicularis. 
Rubus  deliciosus. 
Eristalis  meigeni: 

Potentilla  gracilis. 
Eristalis  temporalis: 
Prunus  demissa. 
Rubus  deliciosus. 
Rydbergia  grandiflora. 
Eristalis  tenax : 

Jamesia  americana. 
Erynnis  leonardus  snowi: 
Chamaenerium  angusti- 

folium. 
Monarda  fistulosa. 


Erizoa  olivahs: 

Carduus  hookerianus. 
Exoprosopa  caliptera: 
Rubus  deliciosus. 
Exoprosopa  divisa: 

Sedum  stenopetalum. 
Exoprosopa  volucris: 

Silene  acaulis. 
Foenus  perplexus: 

Geranium  caespitosum. 
Geocoris  bullatus: 

Potentilla  pulcherrima. 
Glypta  sp. : 

Geranium  caespitosum. 
Gnophaela  vermiculata: 
Achillea  millefolium. 
Polygonum  bistorta. 
Potentilla  pulcherrima. 
Rubus  strigosus. 
Solidago  missouriensis. 
Gonochrysis  densa: 

Pentstemon  glaber. 
Grapta  hylas: 

Carduus  hookerianus. 
Halictus  (Chloralictus)  sp.: 
Asclepias  halli. 
Castilleia  miniata. 
Geranium  caespitosum. 
Gilia  aggregata. 
Mertensia  sibirica. 
Monarda  fistulosa. 
Opulaster  opulifolius. 
Pentstemon  glaber. 

gracilis. 
Prunus  demissa. 
Halictus  (Evylaeus)  sp.: 
Apocynum  androsaemi- 

folium. 
Astragalus  drummondi. 
Castilleia  miniata. 
Chamaenerium  angusti- 

folium. 
Mertensia  sibirica. 
Pentstemon  gracilis. 
Prunus  demissa. 
Rosa  acicularis. 
Tradescantia  virginiana. 
Halictus  fendleri: 

Thalictrum  fendleri. 
Halictus  (Lasioglossum)  sp. : 
Asclepias  speciosa. 
Castilleia  miniata. 
Chamaenerium  angusti- 

folium. 
Geranium  caespitosum. 
Monarda  fistulosa. 
Opulaster  opulifolius. 
Prunus  demissa. 
Rubus  deliciosus. 
strigosus. 
Halictus  lerouxi : 


Halictus  medionitens: 

Geranium  caespitosum. 
Holodiscus  dumosus. 


Halictus  medionitens — Con. 
Potentilla  pulcherrima. 
Rosa  acicularis. 
Rubus  deliciosus. 
Halictus  manitonellus : 
Monarda  fistulosa. 
Rosa  acicularis. 
Halictus  pulzenua: 

Castilleia  miniata. 
Chamaenerium  angusti- 

folium. 
Frasera  speciosa. 
Geranium  caespitosum. 
richardsoni. 
Gilia  aggregata. 
Mertensia  sibirica. 
Monarda  fistulosa. 
Opulaster  opulifolius. 
Pentstemon  glaber. 
gracilis, 
halli. 

secundiflorus. 

Prunus  demissa. 

Rosa  acicularis. 

Rubus  deliciosus. 

strigosus. 

Halicyoides  mamus: 

Achillea  millefolium. 
Hammerschmidtia  ferruginea: 
Geranium  caespitosum. 
Heracleum  lanatum. 
Holodiscus  dumosus. 
Heriades  gracilior: 
Fragaria  vesca. 
Pentstemon  glaber. 
gracilis. 
Heringia  salix : 

Rubus  deliciosus. 
Hyloicus  separatus : 

Pachylophus  caespitosus. 
Irbisia  brachycerus: 
Caltha  leptosepala. 
Drymocallis  fissa. 
Geranium  caespitosum. 
Jamesia  americana. 
Malvastrum  cocineum. 
Lemonias  nubigena  wheeleri : 
Geranium  caespitosum. 
Helianthus  petiolaris. 
Rydbergia  grandiflora. 
Leptura  chrysocoma: 

Sambucus  racemosa. 
Lithargus  apicalis  opuntiae: 

Stanleya  pinnatifida. 
Lycaena  glaucon: 

Galium  borealis. 
Lycaena  pseudargiolus: 

Geranium  caespitosum. 
Lygus  pratensis: 

Ibidium  strictum. 
Mallota  flavoterminata: 

Rosa  acicularis. 
Megachile  gemula  albula: 
Chamaenerium  angusti- 
folium. 
Megachile  pugnata: 

Carduus  hookerianus. 


POLLINATORS   AND   FLOWERS. 


253 


Megachile  pugnata — Con. 

Chamaenerium  angusti- 
folium. 

Erigeron  macranthus. 

Geranium  caespitosum. 

Petalostemon  purpureus. 
Megachile  relativa: 

Chamaenerium  angusti- 
folium. 

Geranium  caespitosum. 
richardsoni. 

Rosa  acicularis. 
Megachile  texana: 

Chamaenerium  angusti- 
folium. 

Rosa  acicularis. 
Megachile  vidua: 

Chamaenerium  angusti- 
folium. 
Megachile  wootoni: 

Astragalus  drummondi. 

Campanula  rotundifolia. 

Carduus  hookerianus. 

Chamaenerium  angusti- 
folium. 

Monarda  fistulosa. 

Opulaster  opulifolius. 

Pentstemon  glaber. 
glaucus. 
gracilis. 

Rosa  acicularis. 

Rubus  deliciosus. 
strigosus. 

Thermopsis  montana. 
Megachile  wootoni  calogaster: 

Chamaenerium  angusti- 
folium. 

Pentstemon  glaber. 

Rosa  acicularis. 

Rubus  deliciosus. 
Melitaea  whitneyi : 

Rydbergia  grandiflora. 
Melitaea  sp. : 

Rubus  deliciosus. 
Melissodes  aurigenia: 

Chamaenerium  angusti- 
folium. 
Melissodes  fremonti: 

Monarda  fistulosa. 

Pentstemon  glaber. 
Melissodes  sp. : 

Carduus  hookerianus. 

Geranium  caespitosum. 
Mesogramma  marginata : 

Potentilla  gracilis. 
Microdon  cothurnatus: 

Prunus  demissa. 
Monumetha  albifrons: 

Apocynum  androsaemi- 
folium. 

Astragalus  drummondi. 

Carduus  hookerianus. 

Chamaenerium  angusti- 
folium. 

Frasera  speciosa. 

Geranium  caespitosum. 

Mertensia  sibirica. 


Monumetha  albifrons — Con. 

Pentstemon  glaber. 
glaucus. 
gracilis, 
halli. 

Rosa  acicularis. 

Rubus  deliciosus. 
Monumetha  argentif rons : 

Chamaenerium  angusti- 
folium. 
Mordella  melaena: 

Solidago  missouriensis. 
Myopa  clausa: 

Rubus  deliciosus. 
Nathalis  iole: 

Potentilla  pulcherrima. 
Nomada  sp. : 

Prunus  virginiana. 

Rubus  deliciosus. 
Odynerus  annulatus: 

Campanula  rotundifolia. 

Stanleya  pinnatifida. 
Omalus  sp. : 

Pentstemon  glaber. 
Ophion  sp.: 

Caltha  leptosepala. 
Osmia  abnormis : 

Iris  missouriensis. 
Osmia  albolateralis : 

Mertensia  pratensis. 
Osmia  bella: 

Iris  missouriensis. 
Osmia  brevij: 

Mertensia  pratensis. 
Osmia  bruneri: 

ElephanteUa  groenlandica. 

Geranium  caespitosum. 

Opulaster  opulifolius. 

Pentstemon  glaber. 
gracilis, 
secundiflorus. 

Rosa  acicularis. 
Osmia  coloradella: 

Mertensia  sibirica. 

Pentstemon  glaber. 
Osmia  densa. : 

Capnoides  aureum. 

Geranium  caespitosum. 

Mertensia  pratensis. 
sibirica. 

Opulaster  opulifolius. 

Pentstemon  glaber. 
gracilis, 
halli. 

Rosa  acicularis. 
Osmia  fulgida: 

Fragaria  vesca. 

Geranium  richardsoni. 

Rosa  acicularis. 

Rubus  deliciosus. 
Osmia  hypoleuca: 

Mertensia  pratensis. 

Pentstemon  gracilis. 

Silene  halli. 
Osmia  megacephala : 

Rydbergia  grandiflora. 


Osmia  melanotricha: 

Mertensia  pratensis. 

Pentstemon  glaber. 
glaucus. 
gracilis, 
halli. 

Rosa  acicularis. 
Osmia  nigrif rons : 

Mertensia  pratensis. 
sibirica. 
Osmia  pentstemonis : 

Mertensia  sibirica. 

Pentstemon  glaucus. 
gracilis, 
secundiflorus. 
Osmia  phaceliae : 

Geranium  caespitosum. 

Mertensia  sibirica. 

Pentstemon  glaber. 
gracilis, 
halli. 
Osmia  propinqua: 

Geranium  caespitosum. 

Rosa  acicularis. 

Rubus  deliciosus. 
strigosus. 

Taraxacum  officinale. 
Osmia  pusilla: 

Mertensia  pratensis. 
Osmia  rohweri : 

Mertensia  pratensis. 
Osmia  wardiana: 

Chamaenerium  angusti- 
folium. 
Osmia  sp. : 

Geranium  caespitosum. 

Monarda  fistulosa. 

Thermopsis  montana. 
Oxybelus  sp. : 

Pentstemon  glaber. 
Panurginus  cressoniellus: 

Erigeron  macranthus. 

Geranium  caespitosum. 

Ibidium  strictum. 

Rosa  acicularis. 

Rubus  deliciosus. 
Panzeria  radicum : 

Achillea  millefolium. 

Erigeron  macranthus. 
Papilio  rutulus: 

Pentstemon  glaber. 
Paragus  bicolor: 

Sieversia  turbinata. 
Parnassius  clodius: 

Carduus  hookerianus. 

Erigeron  macranthus. 
Parnassius  smintheus: 

Allium  recurvatum. 

Drymocallis  fissa. 

Geranium  caespitosum. 

Iris  missouriensis. 

Pentstemon  secundiflorus. 

Potentilla  pulcherrima. 
Peleteria  robusta: 

Erigeron  macranthus. 
Phorbia  fusciceps: 

Erigeron  macranthus. 


254 


EXPERIMENTAL   POLLINATION. 


Phorbia  fusciceps — Con. 
Holodiscus  dumosus. 
Potentilla  pulcherrima. 
Phormia  regina: 

Pentstemon  gracilis. 
Tradescantia  virginiana. 
Phyciodes  camillus: 
Rubus  deliciosus. 
Sedum  stenoptetalum. 
Pieris  protodice: 

Sedum  stenopetalum. 
Pieris  sisymbri : 

Carduus  hookerianua. 
Pipiza  vanduzeei: 

Rubus  deliciosus. 
Pipiza  sp. : 

Rosa  acicularis. 
Rubus  deliciosus. 
Pompiloides  sp. : 

Pentstemon  glaber. 
Stanleya  pinnatifida. 
Prosopis  basalis: 

Chamaenerion  angusti- 

folium. 
Geranium  caespitosum. 
Pentstemon  gracilis, 
halli. 

secundiflorus. 
Rosa  acicularis. 
Rubus  deliciosus. 
Prosopis  coloradensis: 

Rosa  acicularis. 
Prosopis  cressoni: 

Rubus  deliciosus. 
Prosopis  elliptica: 

Apocynum  androsaemi- 

folium. 
Chamaenerium  angusti- 

folium. 
Dasyphora  fruticosa. 
Erigeron  macranthus. 
Geranium  caespitosum. 
richardsoni. 
Monarda  fistulosa. 
Pentstemon  glaber. 
glaucus. 
gracilis, 
secundiflorus 
Rosa  acicularis. 
Rubus  deliciosus. 
Prosopis  episcopalis : 
Galium  boreale. 
Pentstemon  glaber. 
Rubus  strigosus. 
Prosopis  tridentula: 

Geranium  caespitosum. 
Prosopis  varifrons: 

Apocynum  androsaemi- 

folium. 
Geranium  caespitosum. 
richardsoni. 
Holodiscus  dumosus. 
Opulaster  opulifolius. 
Pentstemon  glaber. 
gracilis, 
unilateralis. 
Rubus  deliciosus. 


Prosopis  varifrons — Con. 
Rubus  strigosus. 
Rosa  acicularis. 
Prosopis  wootoni: 

Geranium  caespitosum. 
Pentstemon  glaber. 
Rosa  acicularis. 
Rubus  deliciosus. 
Prosopis  sp. : 

Solidago  missouriensis. 
Protoparce  quinquemaculatus 
Pachylophus  caespitosus. 
Protothyreopus  dilectus: 

Geranium  caespitosum. 
Psammophila  violacepennis: 
Geranium  caespitosum. 
Pseudomasaris  vespoides : 
Calochortus  gunnisoni. 
Geranium  caespitosum. 
Mertensia  sibirica. 
Monarda  fistulosa. 
Opulaster  opulifolius. 
Prunus  demissa. 
Pentstemon  glaber. 
glaucus. 
gracilis. 
Rubus  deliciosus. 
strigosus. 
Pseudomelecta    californica 
miranda: 
Asclepias  halli. 
Psithyrus  ashtoni: 

Chamaenerium  angusti- 

folium. 
Geranium  caespitosum. 
Psithyrus  consultus: 

Delphinium  scopulorum. 
Monarda  fistulosa. 
Solidago  missouriensis. 
Psithyrus  f ernaldae : 

Carduus  hookerianus. 
Psithyrus  insularis: 

Aquilegia  coerulea. 
Carduus  hookerianus. 
Chamaenerium  angusti- 

folium. 
Dasyphora  fruticosa. 
Gentiana  parryi. 
Geranium  caespitosum. 
Ptilodexia  harpasa: 

Prunus  demissa. 
Pyrameis  atlanta: 

Carduus  hookerianus. 
Linaria  vulgaris. 
Satyrus  charon: 

Carduus  hookerianus. 
Erigeron  macranthus. 
Sedum  stenopetalum. 
Scaba  opinator: 

Mertensia  sibirica. 
Selasphorus  platycercus: 
Castilleia  miniata. 
Iris  missouriensis. 
Mertensia  sibirica. 
Monarda  fistulosa. 
Pentstemon  gracilis. 

secundiflorus 


Solenius  sp. : 

Chamaenerium  angusti- 
folium. 
Specomyia  vittata: 

Prunus  demissa. 
Spegina  infuscata: 

Prunus  demissa. 
Sphaerophoria  cylindrica: 

Rosa  acicularis. 
Sphecodes  sophiae: 

Chamaenerium  angusti- 

folium. 
Lappula  floribunda. 
Potentilla  arguta. 
gracilis. 
Prunus  pennsylvanica. 

virginiana. 
Valeriana  edulis. 
Sphex  vulgaris: 

Geranium  caespitosum. 
Sterictophora  sp. : 

Petalostemon  candidus. 
Synanthedon  albicornis: 
Achillea  millefolium. 
Rubus  strigosus. 
Syritta  pipiens: 

Prunus  demissa. 
Syrphus  amalopis: 

Geranium  caespitosum. 
Syrphus  americanus: 
Asclepias  halli. 
Chamaenerium  angusti- 

folium. 
Frasera  speciosa. 
Geranium  caespitosum. 
Pentstemon  gracilis. 
Rosa  acicularis. 
Rubus  deliciosus. 
strigosus. 
Tradescantia  virginiana. 
Syrphus  disgregus: 

Prunus  demissa. 
Syrphus  nitens: 

Rubus  deliciosus. 
Syrphus  opinator: 
Gentiana  parryi. 
Geranium  caespitosum. 
Pentstemon  gracilis. 

secundiflorus. 
Rosa  acicularis. 
Systoechus  vulgaris: 

Pentstemon  gracilis. 
Rosa  acicularis. 
Rubus  deliciosus. 
Tabanus  rhombicus: 

Geranium  caespitosum. 
Temnostoma  aequale: 
Rubus  deliciosus. 
Tenthredella  unicincta : 
Erigeron  macranthus. 
Pentstemon  glaber. 
Tenthredella  flavomarginis: 

Heracleum  lanatum. 
Tetrachrysis  lauta : 

Pentstemon  glaber. 


POLLINATORS   AND   FLOWERS. 


255 


Tetraopee  sp.: 

Asclepias  halli. 
Thanaos  martialis: 

Chamaenerium  angusti- 
folium. 

Delphinium  scopulorum. 

Erigeron  macranthus. 

Geranium  caespitosum. 
richardsoni. 

Mertensia  sibirica. 

Monarda  nstulosa. 

Pentstemon  glaber. 
Thanaos  propertius: 

Capnoides  aureum. 
Theventimtia  muricatus: 

Prunus  demissa. 
Thyreocoriaanthracina : 

Frasera  speciosa. 

Physaria  didymocarpa. 


Titusella  pronitens: 

Pentstemon  glaber. 
gracilis. 
Trichius  affinis: 

Calochortus  gunnisoni. 
Trichodes  ornatus: 

Rubus  deliciosus. 
Trichopticus  septentrionalis : 

Rubus  deliciosus. 
Triepeolus  helianthi  grandior: 

Asclepias  halli. 
Trypeta  occidentalis : 

Achillea  millefolium. 
Vespa  germanica: 

Chamaenerium  angusti- 
folium. 

Jamesia  americana. 

Mertensia  sibirica. 

Monarda  nstulosa. 

Opulaster  opulifolius. 

Pentstemon  glaber. 

unilateralis. 


Vespa  occidentalis: 

Erigeron  macranthus. 

Linaria  vulgaris. 
Volucella  rufomaculata: 

Castilleia  miniata. 

Rubus  deliciosus. 
strigosus. 
Volucella  satur: 

Rubus  deliciosus. 

Stanleya  pinnatifida. 
Xylota  angustiventris: 

Heracleum  lanatum. 
Xylota  flavitibia: 

Holodiscus  dumosus. 

Rosa  acicularis. 

Rubus  deliciosus. 
Xylota  nigra: 

Rosa  acicularis. 
Zodion  pygmaeum: 

Prunus  demissa. 


6.     FLOWERS  AND  THEIR  VISITORS. 


Achillea  millefolium: 
Agathis  vulgaris. 
Chrysophanus  helloides. 
Gnophaela  vermiculata. 
Halicyoides  mamus. 
Panzeria  radicum. 
Synanthedon  albicornis. 
Trypeta  occidentalis. 
Aconitum  columbianum: 
Bombus  appositus. 
bifarius. 
edwardsi. 
flavifrons. 
juxtu3. 
occidentalis. 
rufocinctus. 
Allium  recurvatum: 
Bombus  edwardsi. 

occidentalis. 
Parnassius  smintheus. 
Apocynum  androsaemifolium : 
Halictus  (Evylaeus)  sp. 
Monumetha  albifrons. 
Prosopis  elliptica. 
varifrons. 
Aquilegia  brevistyla: 

Bombus  hunti. 

Aquilegia  coerulea: 

Bombus  hunti. 

occidentalis. 
Clisodon  terminalis. 
Psithyrus  insularis. 
Aragalus  lamberti: 

Anthophora  simillima. 
Arctostaphylus  uva-ursi : 
Apis  mellifica. 
Bombus  edwardsi. 
Asclepias  halli: 
Apis  mellifica. 
Bembex  spinolae. 
Halictus  (Chloralictus)  sp. 
Pseudomelecta  miranda. 
Syrphus  americanus. 
Tetraopes  sp. 
Triepeolus     helianthi 
grandior. 
Asclepias  speciosa: 
Apis  mellifica. 
Echinomyia  decisa. 
Halictus  (Lasioglossum)sp. 
Astragalus  drummondi: 
Andrena  gardineri. 
imitatrix. 
vicina. 
Bombus  edwardsi. 
fervidus. 
hunti. 
juxtus. 
morrisoni. 
Halictus  (Evylaeus)  sp. 
Megachile  wootoni. 
Monumetha  albifrons. 


Aster  f oliaceus : 

Bombus  edwardsi. 

flavifrons. 

Calochortus  gunnisoni: 

Bombus  edwardsi. 

flavifrons. 

occidentalis. 

rufocinctus. 
Curtipogon  leucozona. 
Dasyllis  fernaldi. 
Panurginus  sp. 
Pseudomasaris  vespoides. 
Trichius  affinis. 
Caltha  leptosepala: 

Irbisia  brachycerus. 
Ophion  sp. 
Campanula  rotundifolia: 
Anthophora  smithi. 
Bombus  edwardsi. 

hunti. 

juxtus. 
Chrysophanus  rubidus. 
Megachile  wootoni. 
Odynerus  annulatus. 
Capnoides  aureum: 

Anthophora  simillima. 
Atrytone  taxiles. 
Bombomelecta  fulvida. 
Bombus  dorsalis. 

juxtus. 

occidentalis. 
Colletes  oromontis. 
Osmia  densa. 
Thanaos  propertius. 
Carduus  hookerianus: 

Acmaeops  longicornis. 
Andrena  crataegi. 
Andronicus  sp. 
Bombus  appositus. 

bifarius. 

edwardsi. 

hunti. 

juxtus. 

nevadensis. 

occidentalis. 
Chrysophanus  rubidus. 
Clisodon  terminalis. 

sp. 
Colias  edwardsi. 
scudderi. 
Epalpus  bicolor. 

rufus. 
Erizoa  olivalis. 
Grapta  hylas. 
Megachile  pugnata. 
wootoni. 
sp. 
Melissodes  sp. 
Monumetha  albifrons. 
Parnassius  clodius. 
Pieris  sisymbri. 
Psithyrus  fernaldae. 
insularis. 

256 


Carduus  hookerianus — Con. 
Pyrameis  atlanta. 
Satyrus  charon. 
Castilleia  miniata: 
Bombus  hunti. 

kirbyellus. 
occidentalis. 
Colias  keewaydinus. 
Halictus  ^Chloralictus)  sp. 
(Evylaeus)  sp. 
(Lasioglossum) 

sp. 

pulzenus. 

Selasphorus  platycercus. 

Volucella  rufomaculata. 

Chamaenerium  angustifolium: 

Anthophora  occidentalis. 

smithi. 
Apis  mellifica. 
Argynnis  atlantis. 
Atrytone  taxiles. 
Bombus  appositus. 
bifarius. 
centralis, 
edwardsi. 
flavifrons. 
hunti. 
juxtus. 
nevadensis. 
occidentalis. 
rufocinctus. 
Clisodon  terminalis. 
Coelioxys  moesta. 
Ctenucha  sp. 
Dasyllis  fernaldi. 
Dejeania  vexatrix. 
Dolichovespula  arctica. 

diabolica. 
Echinomyia  algens. 
Erynnis  leonardus  snowi. 
Halictus  (Evylaeus)  sp. 
(Lasioglossum) 

sp. 
pulzenus. 
Megachile  gemula  albula. 
pugnata. 
relativa. 
texana. 
vidua, 
wootoni. 
wootoni  calo- 
gaster. 
Melissodes  aurigenia. 
Monumetha  albifrons. 

argentifrons. 
Osmia  wardiana. 
Prosopis  basalis. 

elliptica. 
Psithyrus  ashtoni. 
insularis. 
Solenius  sp. 
Sphecodes  sophiae. 
Syrphus  americanus. 


FLOWERS   AND   VISITORS. 


257 


hamaenerium  angustifolium 
—Con. 

Thanaos  martialis. 
Vespa  germanica. 
Chrysopais  villosa: 

Bombus  edwardsi. 

juxtus. 
Echinomyia  algens. 
Cleome  serrulata: 

Bombus  edwardsi. 

Eliphilus  latifrons. 

Clementsia  rhodantha: 

Anthomyia  sp. 
Daeyphora  fruticosa: 
Bombus  flavifrons. 
Brenthis  triclaris. 
Coenonympha  pamphi- 

loides. 
Erebia  epipsodea. 
Prosopis  elliptica. 
Psithyrus  insularis. 
Delphinium  scopulorum: 
Bombus  appositus. 
bifarius. 
centralis, 
edwardsi. 
flavifrons. 
juxtus. 
morrisoni. 
occidentalis. 
Dolichovespula  arctica. 
Psithyrus  consultus. 
Thanaos  martialis. 
Dodocatheon  meadia: 

Anthophora  simillima. 
Bombus  bifarius. 
edwardsi. 
flavifrons. 
Draba  aurea: 

Chionobis  macouni. 
Drymocallis  fissa: 

Bombus  edwardsi. 
Irbisia  brachycerus. 
Parnassius  smintheus. 
Elephantella  groenlandica: 
Bombus  bifarius. 
Osmia  bruneri. 
Erigeron  macranthus: 

Andrena  apacheorum. 
Anthrax  fulviana. 

tegminipennis. 
Argynnis  atlantis. 
Bombus  bifarius. 
edwardsi. 
hunti. 
Bracon  helena. 
Brenthis  helena. 
Chrysophanus  helloides. 
Coenonympha  pamphi- 

loides. 
Megachile  pugnata. 
Parnassius  clodius. 
Panurginus  cressoniellus. 
Panzeria  radicum. 
Peleteria  robusta. 
Prosopis  elliptica. 


Erigeron  macranthus — Con. 
Satyrus  charon. 
Tenthredella  unicincta. 
Thanaos  martialis. 
Vespa  occidentalis. 
Erigeron  uniflorus: 
Bombus  hunti. 

occidentalis. 
Erysimum  asperum: 

Bombus  occidentalis. 
Fragaria  vesca: 

Bombus  edwardsi. 
Heriades  gracilior. 
Osmia  fulgida. 
Frasera  speciosa: 
Apis  mellifica. 
Andrena  crataegi. 

madronitens. 
Bombus  edwardsi. 

flavifrons. 

hunti. 

juxtus. 
Clisodon  terminalis. 
Halictus  lerouxi. 

pulzenus. 

sp. 
Monumetha  albifrons. 
Syrphus  americanus. 
Thyreocoris  anthracina. 
Galium  boreale: 

Lycaena  glaucon. 
Prosopis  episcopalis. 
Geum  rivale: 

Archytas  sp. 
Gentiana  parryi: 

Bombus  appositus. 

juxtus. 

nevadensis. 
Psithyrus  insularis. 
Syrphus  opinator. 
Geranium  caespitosum: 
Ancistrocerus  sp. 
Andrena  apacheorum. 

braccata. 

madronitens. 

vicina. 
Andronicus  sp. 
Apanteles  sp. 
Apis  mellifica. 
Argynnis  eurynome. 
Bombus  appositus. 

bifarius. 

edwardsi. 

hunti. 

juxtus. 

occidentalis. 

rufocinctus. 
Cenis  uhleri. 
Clisodon  terminalis. 
Coelioxys  moesta. 
Colletes  kincaidi. 

oromontis. 

sieverti. 
Epeolus  helianthi. 
Erebia  epipsodea. 
Foenus  perplexus. 


Geranium  caespitosum — Con. 
Glypta  sp. 

Halictus  (Chloralictus)  sp. 
(Lasioglossum) 

sp. 
medionitens. 
pulzenus. 
Hammerschmidtia  ferru- 

ginea. 
Irbisia  brachycerus. 
Lemonias  nubigena 

wheeleri. 
Lycaena  pseudargiolus. 
Megachile  pugnata. 
relativa. 
Melissodes  sp. 
Monumetha  albifrons. 
Osmia  bruneri. 


phaceliae. 

propinqua. 

sp. 
Panurginus  cressoniellus. 
Parnassius  smintheus. 
Protothyreopus  dilectus. 
Prosopis  basalis. 

elliptica. 

tridentula. 

varifrons. 

wootoni. 
Psammophila      violace- 

pennis. 
Pseudomasaris  vespoides. 
Psithyrus  insularis. 
Sphex  vulgaris. 
Syrphus  amalopis. 

americanus. 

opinator. 
Tabanus  rhombicus. 
Thanaos  martialis. 
Geranium  richardsoni: 
Ancistrocerus  sp. 
Andrena  madronitens. 
Apis  mellifica. 
Bombus  bifarius. 

hunti. 

occidentalis. 
Ectemius  montanus. 
Halictus  pulzenus. 
Megachile  relativa. 
Osmia  fulgida. 
Prosopis  elliptica. 

varifrons. 
Thanaos  martialis. 
Gilia  aggregata: 

Halictus  (Chloralictus)  sp. 

pulzenus. 
Helianthus  petiolaris : 
Argynnis  eurynome. 
Bombus  hunti. 
Lemonias  nubigena 
wheeleri. 
Heracleum  lanatum : 

Anthrax  hypomelas. 


258 


EXPERIMENTAL   POLLINATION. 


Heracleum  lanatum — Con. 
Bombus  occidentalia. 
Echinomyia  algena. 
Eclimus  muricatus. 
Hammerschmidtia  ferru- 

ginea. 
Tenthredella  flavomar- 

ginis. 
Xylota  angustiventris. 
Holodiscus  dumosus: 
Andrena  crataegi. 

madronitena. 
Anthrax  alternata. 
Apis  mellifica. 
Bombus  bifarius. 
edwardsi. 
hunti. 
juxtus. 
occidentalis. 
Chrysotoxum  integrum. 
Clisodon  terminalis. 
Colletes  oromontis. 
Halictus  medionitens. 
Hammerschmidtia  ferru- 

ginea. 
Phorbia  fusciceps. 
Prosopis  varifrons. 
Xylota  flavitibia. 
Ibidium  strictum: 

Bombus  appositus. 
morrisoni. 
Halictus  sp. 
Lygus  pratensis. 
Panurginus  cressoniellus. 
Iris  missouriensis: 

Chionobis  macouni. 
Osmia  abnormis. 

bella. 
Parnassius  smintheus. 
Selasphorus  platycercus. 
Jamesia  americana: 
Andrena  edwiniae. 
Ancistrocerus  sp. 
Apis  mellifica. 
Bombus  bifarius. 
edwardsi. 
hunti. 
juxtus. 
occidentalis. 
Eristalis  tenax. 
Irbisia  brachycerus. 
Vespa  germanica. 
Lappula  floribunda: 

Sphecodes  sophiae. 
Lathyrus  ornatus: 

Bombus  edwardsi. 
Linaria  vulgaris: 
Apis  mellifica. 
Basilarchia  weidemeyeri. 
Bombus  occidentalis. 
Pyrameis  atlanta. 
Vespa  occidentalis. 
Lithospermum  canescens: 

Anthophora  simillima. 
Malvastrum  coccineum: 

Agapostemon  splendens. 
Irbisia  brachycerus. 


Mentzelia  multiflora: 
Apis  mellifica. 
Bombus  bifarius. 
juxtus. 
occidentalis. 
Mertensia  pratensis: 

Clisodon  terminalis. 
Colletes  oromontis. 
Osmia  albolateralis. 
brevis. 
densa. 
hypoleuca. 
melanotricha. 
nigrifrons. 
pentstemonis. 
pusilla. 
rohweri. 
Mertensia  sibirica: 

Acmaeops  longicornis. 
Ancistrocerus  sp. 
Andrena  madronitens. 
Bombus  bifarius. 
edwardsi. 
flavifrons. 
ftflvida. 
juxtus. 
occidentalis. 
Bombomelecta  fulvida. 
Ceratina  sp. 
Clisodon  sp. 
Colletes  oromontis. 

sp. 
Dejeania  vexatrix. 
Halictus  (Chloralictus)  sp. 
(Evylaeus)  sp. 
pulzenus. 
Monumetha  albifrona. 
Osmia  coloradella. 
densa. 
nigrifrons. 
pentstemonis. 
phaceliae. 
Pseudomasaris  vespoidea. 
Scaba  opinator. 
Selasphorus  platycercus. 
Thanaos  martialis. 
Vespa  germanica. 
Monarda  fistulosa: 
Andrena  crataegi. 
Anthophora  smithi. 
Argynnis  atlantis. 
Atrytone  taxiles. 
Bombus  appositus. 
bifarius. 
centralis, 
fervidus. 
flavifrona. 
hunti. 
morrisoni. 
occidentalis. 
pennsylvanica. 
Chrysophanus  sirius. 
Clisodon  termininalis. 
Colletes  oromontis. 
Ctenucha  sp. 
Erynnia  leonardus  snowi. 


Monarda  fistulosa — Con. 

Halictus  (Chloralictus)  sp. 
(Lasioglossum) 

sp. 
manitonellus. 
pulzenus. 
Megachile  wootoni. 
Melissodes  fremonti. 
Osmia  sp. 
Prosopis  elliptica. 
Pseudomasaris  vespoidea. 
Psithyrus  consultua. 
Selasphorus  platycercua. 
Thanaos  martialis. 
Vespa  germanica. 
Onagra  biennis : 

Andrena  madronitena. 
Bombus  juxtus. 
Megachile  sp. 
Opulaster  opulifolius : 
Andrena  crataegi. 

madronitens. 
Apis  mellifica. 
Bombus  edwardsi. 
nevadensia. 
occidentalis. 
Dejeania  vexatrix. 
Eristalis  latifrons. 
Halictus  (Chloralictus)  sp. 
(Lasioglossum) 

sp. 
pulzenus. 
Megachile  wootoni. 
Osmia  bruneri. 

densa. 
Prosopis  varifrons. 
Pseudomasaris  vespoides. 
Vespa  germanica. 
Oreochrysum  parryi : 

Chrysophanus  helloides. 
Pachylophus  caespitosus: 
Celerio  lineata. 
Hyloicus  separatua. 
Protoparce  quinquemac- 
ulatus. 
Pedicularis  parryi : 
Bombus  hunti. 

kirbyellus. 
Pedicularis  racemosa : 
Bombus  edwardsi. 

occidentalia. 
Pentstemon  glaber: 

Agapostemon  splendena. 
Andrena  madronitena. 
prunorum. 
vicina. 
Anthophora  bomboidea. 

simillima. 
Apis  mellifica. 
Atrytone  taxiles. 
Bombus  appositus. 
bifarius. 
centralis, 
edwardsi. 
hunti. 
juxtus. 
kirbyellus. 


FLOWERS   AND   VISITORS. 


259 


Pentstemon  glaber — Con. 
Bombus  morrisoni. 

occidentalis. 

rufocinctus. 
Bombomelecta  fulvida. 
Celerio  lineata. 
Clisodon  terminalis. 

sp. 
Gonochrysis  densa. 
Halictus  (Chloralictus)  sp. 

pulzenus. 
Heriades  gracilior. 
Megachile  wootoni. 

wootoni  calo- 
gaster. 
Melissodes  fremonti. 
Monumetha  albifrons. 
Omalus  sp. 
Osmia  bruneri. 

coloradella. 
densa. 

melanotricha. 
phaceliae. 
Oxybelus  sp. 
Panurginus  sp. 
Papilio  rutulus. 
Pompiloides  sp. 
Prosopis  elliptica. 

episcopalis. 

varifrons. 

wootoni. 
Pseudomasaris  vespoidea. 
Tetrachrysis  lauta. 
Tenthredella  unicincta. 
Thanaos  martialis. 
Titusella  pronitens. 
Vespa  germanica. 
Xylota  angustiventris. 
Pentstemon  glaucus: 
Bombus  bifarius. 

edwardsi. 

juxtus. 

morrisoni. 

occidentalis. 
Clisodon  terminalis. 
Megachile  wootoni. 
Monumetha  albifrons. 
Osmia  melanotricha. 
pentstemonis. 
Prosopis  elliptica. 
Pseudomasaris  vespoides. 
Pentstemon  gracilis: 

Andrena  washingtoni. 
Andronicus  sp. 
Anthophora  neomexi- 

cana. 
Anthophora  simillima. 
Bombus  appositus. 

bifarius. 

centralis. 

edwardsi. 

hunti. 

juxtus. 

morrisoni. 

rufocinctus. 
Bombomelecta  fulvida. 


Pentstemon  gracilis — Con. 
Ceratina  sp. 
Cerastomia  lignaria. 
Clisodon  terminalis. 

sp. 
Colletes  kincaidi. 
Halictus  (Chloralictus)  sp. 

(Evylaeus)  sp. 

pulzenus. 
Heriades  gracilior. 
Megachile  wootoni  calo- 

gaster. 
Monumetha  albifrons. 
Osmia  bruneri. 


hypoleuca. 
melanotricha. 
pentstemonis. 
phaceliae. 
Phormia  regina. 
Prosopis  basalis. 
elliptica. 
varifrons. 
Pseudomasaris  vespoides. 
Selasphorus  platycercus. 
Syrphus  americanus. 

opinator. 
Systoechus  vulgaris. 
Titusella  pronitens. 
Penstemon  halli: 

Anthophora  simillima. 
Halictus  pulzenus. 
Osmia  densa. 

melanotricha. 
phaceliae. 
Monumetha  albifrons. 
Prosopis  basalis. 
Penstemon  secundifiorus : 
Andrena  madronitens. 
Anthophora  simillima. 
Argynnis  atlantis. 
Bombus  bifarius. 
edwardsi. 
juxtus. 
occidentalis. 
Clisodon  terminalis. 
Halictus  pulzenus. 
Osmia  bruneri. 

pentstemonis. 
Parnassius  smintheus. 
Prosopis  basalis. 

elliptica. 
Selasphorus  platycercus. 
Syrphus  opinator. 
Pentstemon  unilateralis: 
Anthophora  simillima. 
Apis  mellihca. 
Bombus  americanorum. 
fervidus. 
juxtus. 
Prosopis  varifrons. 
Vespa  germanica. 
Petalostemon  candidus: 
Apis  mellifica. 
Bombus  appositus. 
edwardsi. 
fervidus. 


Petalostemon  candidus — Con. 
Bombus  hunti. 

rufocinctus. 
Sterictophora  sp. 
Petalostemon  purpureus: 
Apis  mellifica. 
Bombus  appositus. 

edwardsi. 

fervidus. 

hunti. 

occidentalis. 

rufocinctus. 
Clisodon  terminalis. 
Colletes  kincaidi. 
Megachile  pugnata. 
sp. 
Phacelia  heterophylla : 

Chrysophanus  rubidus. 
Physaria  didymocarpa: 
Halictus  sp. 

Thyreocoris  anthracina. 
Polygonum  bistorta: 

Chrysotoxum  upsilon. 
Epalpus  bicolor. 
Gnophaela  vermiculata. 
Potentilla  arguta: 
Andrena  vicina. 
Bombus  juxtus. 

kirbyellus. 
Sphecodes  sophiae. 
Potentilla  gracilis: 

Anthrax  hypomelas. 
Bombus  hunti. 
Eristalis  meigeni. 
Mesogramma  marginata. 
Sphecodes  sophiae. 
Potentilla  pulcherrima : 
Bombus  kirbyellus. 

occidentalis. 
Chionobis  macouni. 
Chrysotoxum  ventri- 

cosum. 
Colias  alexandra. 
Erebia  epipsodea. 
Geocoris  bullatus. 
Gnophaela  vermiculata. 
Halictus  medionitens. 

sp. 
Nathalis  iole. 
Parnassius  smintheus. 
Prunus  demissa: 

Acmaeops  longicornis. 

pratensis. 
Agapostemon  sp. 
Andrena  canadensis. 

crataegi. 

edwiniae. 

madronitens. 

prunorum. 

vicina. 

sp. 
Bombus  fiavifrons. 

occidentalis. 
Brachyopa  notata. 
Brenthis  triclarius. 
Calliphora  vomitoria. 


260 


EXPERIMENTAL   POLLINATION. 


Prunus  demissa — Con. 
Chilosia  petulca. 

tristis. 
Coenonympha  pamphi- 

loides. 
Colletes  kincaidi. 

oromontis. 
Erebia  epipsodea. 
Eristalis  arbustorum. 
dimidiatus. 
temporalis. 
Halictus  (Chloralictus)  sp. 
(Evylaeus)  sp. 
(Lasioglossum) 

sp. 
pulzenus. 
sp. 
Microdon  cothurnatus. 
Pseudomasaris  vespoides. 
Ptilodexia  harpasa. 
Specomyia  vittata. 
Spegina  infuscata. 
Syrphus  disgregus. 
Syritta  pipiens. 
Thevenetimyia  muricatus. 
Zodion  pygmaeum. 
Prunus  pennsylvanica: 
Sphecodes  sophiae. 
Prunus  virginiana: 
Andrena  crataegi. 
prunorum. 
vicina. 
sp. 
Nomada  sp. 
Sphecodes  sophiae. 
Rosa  acicularis: 

Acmaeops  longicornis. 

pratensis. 
Agapostemon  splendens. 
Andrena  crataegi. 

madronitens. 
vicina. 
washingtoni. 
sp. 
Anthrax  lateralis. 

nigra. 
Anthophora  simillima. 
Apis  mellifica. 
Arctophila  flagrans. 
Bombus  appositus. 
bifarius. 
edwardsi. 
flavifrons. 
hunti. 
juxtus. 
morrisoni. 
occidentalis. 
rufocinctus. 
Bombylius  atriceps. 
Chrysotoxum  integrum. 
Clisodon  terminalis. 
Colletes  americanus. 
Eristalis  latifrons. 
Halictus  (Evylaeus)  sp. 
manitonellus. 
medionitens. 
pulzenus. 
Mallota  flavoterminata. 


Rosa  acicularis — Con. 
Megachile  relativa. 
texana. 
wootoni. 
wootoni  calo- 
gaster. 
Monumetha  albifrons. 
Osmia  bruneri. 
densa. 
fulgida. 
melanotricha. 
propinqua. 
Panurginus  cressionellus. 
Pipiza  sp. 
Prosopis  basalis. 

coloradensis. 
elliptica. 
varifrons. 
wootoni. 
Sphaerophoria  cylindrica. 
Syrphus  americanus. 

opinator. 
Systoechus  vulgaris. 
Xylota  flavitibia. 
nigra. 
Rubus  deliciosus: 

Acmaeops  longicornis. 

pratensis. 
Ancistrocerus  sp. 
Andrena  canadensis, 
crataegi. 
madronitens. 
placida. 
prunorum. 
vicina. 
Andronicus  sp. 
Apis  mellifica. 
Bombus  americanorum. 
appositus. 
bifarius. 
edwardsi. 
fervidus. 
flavifrons. 
hunti. 
juxtus. 
kirbyellus. 
morrisoni. 
occidentalis. 
rufocinctus. 
Brachyopa  notata. 
Chrysogaster  parva. 
Colletes  oromontis. 
Eristalis  flavipes. 
latifrons. 
temporalis. 
Exoprosopa  caliptera. 
Halictus  (Lasioglossum) 
sp. 
medionitens. 
pulzenus. 
sp. 
Heringia  salix. 
Megachile  wootoni. 

wootoni  calo- 
gaster. 
Melitaea  sp. 
Monumetha  albifrons. 
Myopa  clausa. 


Rubus  deliciosus — Con. 
Nomada  sp. 
Osmia  fulgida. 

propinqua. 
Panurginus  cressionellus. 

sp. 
Phyciodes  camillus. 
Pipiza  vanduzeei. 

sp. 
Prosopis  basalis. 
cressoni. 
elliptica. 
varifrons. 
wootoni. 
Pseudomasaris  vespoides. 
Systoechus  vulgaris. 
Syrphus  americanus. 

nitens. 
Temnostoma  aequale. 
Tricopticus  septen- 

trionalis. 
Trichodes  ornatus. 
Volucella  rufomaculata. 

satur. 
Xylota  flavitibia. 
Rubus  strigosus: 

Ancistrocerus  sp. 
Andrena  crataegi. 
lewisi. 

madronitens. 
vicina. 
Anthophora  simillima. 
Apis  mellifica. 
Bombus  bifarius. 
edwardsi. 
flavifrons. 
hunti. 
juxtus. 
morrisoni. 
occidentalis. 
Clisodon  terminalis. 
Colletes  oromontis. 
Eristalis  arbustorum. 
Gnophaela  vermiculata. 
Halictus  (Lasioglossum) 
sp. 
pulzenus. 
sp. 
Megachile  wootoni. 
Osmia  propinqua. 
Prosopis  episcopalis. 

varifrons. 
Pseudomasaris  vespoides. 
Synthedon  albicornis. 
Syrphus  americanus. 
Volucella  rufomaculata. 
Rydbergia  grandiflora: 
Argynnis  eurynome. 
Bombus  appositus. 
edwardsi. 
flavifrons. 
hunti. 
Eristalis  temporalis. 
Lemonias  nubigena 

wheeleri. 
Melitaea  whitneyi. 
Osmia  megacephala. 


FLOWERS   AND  VISITORS. 


261 


Sambucus  racemosa: 

Leptura  chrysocoma. 
Scutellaria  resinosa: 

Bombus  morrisoni. 
Sedum  stenopetalum: 

Andrena  madronitens. 

Anthidium  tenuiflorae. 

Anthrax  sinuosa. 

Argynnis  eurynome. 

Bombus  edwardsi. 
hunti. 

Exoprosopa  divisa. 

Phyciodes  camillus. 

Pieris  protodice. 

Satyrus  charon. 
Sieversia  ciliata: 

Bombus  edwardsi. 

occidentalis. 

Halictus  sp. 
Sieversia  turbinata: 

Paragus  bicolor. 
Silene  acaulis: 

Exoprosopa  volucris. 
Silene  halli: 

Osmia  hypoleuca. 
Solidago  missouriensis: 

Anthrax  halcyon. 

Apis  mellifica. 

Bombus  edwardsi. 


Solidago  missouriensis — Con. 
Bombus  flavifrons. 

hunti. 

occidentalis. 

rufocinctus. 
Colletes  americanus. 

oromontis. 
Epalpus  bicolor. 
Gnophaela  vermiculata. 
Halictus  sp. 
Mordella  melaena. 
Prosopis  sp. 
Psithyrus  consultus. 
Stanleya  pinnatifida: 

Agapostemon  coloraden- 
sis. 

sp. 
Andrena  vicina. 
Apis  mellifica. 
Bombus  bifarius. 

hunti. 

morrisoni. 

rufocinctus. 
Bracon  vulgaris. 
Ceratina  sp. 
Lithargus  apicalis  opun- 

tiae. 
Odynerus  annulata. 
Pompiloides  sp. 
Volucella  satur. 


Taraxacum  officinale: 

Agapostemon  coloradensis. 
splendens. 

Apis  mellifica. 

Osmia  propinqua. 
Thermopsis  montana: 

Bombus  americanorum. 
hunti. 
juxtus. 

Megachile  wootoni. 

Osmia  sp. 
Thalictrum  fendleri: 

Apis  mellifica. 

Halictus  fendleri. 
sp. 
Tradescantia  virginiana: 

Anthrax  sinuosa. 

Apis  mellifica. 

Halictus  (Evylaeus)  sp. 

Panurginus  sp. 

Phormia  regina. 

Syrphus  americanus. 
Trifolium  dasyphyllum : 

Bombus  hunti. 

kirbyellus. 
Valeriana  edulis: 

Epalpus  rufus. 

Sphecodes  sophiae. 


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INDEX. 


Acer  pseudoplatanus,  151 
Achillea  millefolium,  115 
Acmaeops  longicornis,  63 
Aconitum,  18,  90,  91,  93,  241 

columbianum,  15,  18,  111 

lycoctonum,  16 

napellus,  16 
Agrostis,  150 
Ajuga,  131 

Allium  recurvatum,  106,  137 
Althea  rosea,  137,  161,  188 
Amarantus,  196,  241 
Ammophila,  221 
Ampelopsis,  146,  168 
Anchusa,  162,  164,  193 
Andrena,  101,  104,  134,  181 

crataegi,  27,  28,  30,  31,  37,  79,  97,  105,  106, 
109 

madronitens,  33,  35,  39,  46,  62,  65,  105 

vetula,  175 

vicina,  29,  33,  65,  69,  70,  71 
Anemone,  130 

japonica,  149 
Angelica,  165 
Anoda  triloba,  187 
Anthidium,  131,  147,  151,  153,  154,  157,  181 

manicatum,  155,  239 
Anthophora  acervorum,  176 

pilipes,  243 

simillima,  34,  40,  68,  74,  77,  106,  109,  136, 
155,  181 
Anthoxanthum,  150 
Antirrhinum,  131 

majus,  147,  148,  170,  184 
Apis  mellifica,  27,  28,  30,  31,  32,  33,  39,  40,  46, 
52,  57,  58,  60,  61,  62,  69,  74,  75,  78,  89, 
93,  97,  104,  106,  109,  114,  131,  134,  136, 
148,  149,  150,  153,  155,  157,  160,  161,  162, 
164,  165,  179,  180,  181,  183,  244 
Aporus  fasciatus,  221 

Aquilegia  coerulea,  100,  101,  105,  106,  111 
Arabis,  136 

Argemone  platyceras,  217 
Argynnis  atlantis,  46,  79,  80,  89,  91,  119,  181 
Asparagus,  138 
Asphodius,  226 
Aster,  80,  109,  185 

bigelovi,  85,  106,  115 
Aucuba,  137 

Bembex  labia tus,  221,  222 

mori,  225 
Bombus,  62 

appositus,  88,  89,  91,  119 

bifarius,  15,  16,  17,  18,  20,  21,  22,  33,  35,  39, 
41,  44,  46,  49,  58,  66,  73,  74,  79,  90,  92, 
116,  119,  134 

californicus,  40 

edwardsi,  19,  22,  23,  24,  25,  33,  62,  76 

flavifrons,  33 

hortorum,  158 

hunti,  119 

hypnorum,  158 


Bombus — Continued. 

juxtus,  15,  16,  17,  19,  20,  21,  22,  23,  24,  25, 
26,  29,  30,  34,  36,  37,  38,  39,  41,  43,  44,  45, 
46,  48,  49,  51,  52,  53,  58,  59,  61,  62,  63, 
66,  70,  73,  75,  76,  77,  78,  79,  88,  89,  90, 
91,  92,  93,  101,  105,  110,  116,  119,   134, 
241 
lapidarius,  132,  158 
morrisoni,  23,  29,  76,  77,  SO,  91 
muscorum,  132,  147,  158 
occidentalis,  30,  57,  91,  105,  119 
pennsylvanicus,  79 
pratorum,  141 
proximus,  24,  25,  26,  31,  33,  35,  36,  37,  39, 

46,  76,  77,  79,  80,  134 
silvarum,  132 

terrestris,  132,  141,  147,  149,  158 
terricola,  194 
Bombylius  fimbriatus,  175,  182 

fuliginosus,  205,  206 
Borrago,  159,  175 

officinalis,  175 
Brachypodium,  150 
Brassica,  173 
Bromus,  150 
Bryonia  dioeca,  138,  187 

Calceolaria,  131 

Calliphora,  156 

Callosamia  promethea,  159 

Calluna,  131 

Calochortus  gunnisoni,  115 

Caltha,  131 

Campanula,  61,  62,  92,  106,  115,  240 

Camponotus,  229 

Carabus,  230 

Carex,  150 

Castilleia,  64 

affinis,  64 

linarifolia,  64 

niiniata,  106,  109 
Celerio  lineata,  55 
Centaurea,  130,  133,  169 

cyanus,  148,  162,  170,  171,  184 
Cerceris,  221 

Chalicodoma,  218,  219,  220 
Chamaenerium,  46,  48,  54,  57,  58,  78,  81,  85, 
89,  93,  98,  99,  101,  105,  110,  111,  114,  115, 
116,  119,  239,  241 
Chenopodium  album,  150 
Chrysanthemum,  176,  186 

leueanthemum,  178 
Cirsium  oleraceum,  133 

palustre,  133 
Cistus,  176 

Clematis  jackmanni,  165,  196 
Cleome  serrulata,  95,  98,  99,  101,  104 
Clisodon  terminalis,  36,  38,  58,  68,  69,  70,  71, 

72,  75,  81,  88,  89,  91,  119,  134 
Coelioxys,  40 
Convolvulus,  136 

sepium,  149,  165 
Corylus  avellana,  150 


269 


270 


INDEX. 


Crataegus,  187 

Crocus,  136,  161,  178,  179,  182 

luteus,  161 

sativus,  185 

vernus,  161 
Cucurbita  maxima,  194 
Cytisus,  131 

Dahlia,  145,  147,  148,  149,  152,  157,  168,  172, 
180,  183,  184,  185,  186 

variabilis,  161,  181 
Deiliphila,  159 

elpenor,  175,  192 
Dejeania  vexatrix,  62 
Delphinium  ajacis,  147,  164 

consolida,  23,  147 

elatum,  23 

scopulorum,  22,  93,  111,  115 

tricorne,  23 
Deutzia,  187,  188 
Dianthus  barbatus,  153,  175,  192 

carthusianorum,  132,  151,  164,  175 
Digitalis  purpurea,  147,  148,  151,  169,  194 
Dodecatheon  meadia,  112 
Doronicum  caucasicum,  180 

Echinacea  purpurea,  187 

Elephantella  groenlandica,  112,  114 

Epilobium  spicatum,  131,  184 

Eranthis  nivalis,  178 

Erigeron  macranthus,  115 

Eristalis  tenax,   130,   147,  156,  157,  181,  182, 

183,  191 
Erynnis  leonardus  snowi,  79,  80,  89,  91 
Eschscholtzia,  184,  185 
Eupatorium,  131 

Festuca,  150 
Ficaria,  131 
Fragaria,  62 
Frasera  carolinensis,  59 

speciosa,  61,  92,  93,  95,  98,  99,  111,  240 
Fritillaria,  136 
Formica  fusca,  225 

rufa,  227,  229 
Fumaria  officinalis,  165 

Galium,  206 
Gentiana  parryi,  115 
Geum  intermedium,  131 

rivale,  131 

urbanum,  131 
Geranium,  28,  39,  41,  57,  58,  80,  82,  92,  95, 
99,  104,  115,  119 

caespitosum,  85,  89,  101,  105,  106,  110,  114, 
115,  134 

carolinianum,  40 

maculatum,  40 

richardsoni,  40,  98,  105,  106,  110,  116,  134 
Gerardia  purpurea,  195 
Gilia  aggregata,  82,  85,  110,  115,  119 
Glycine,  167 

Halictus,  27,  28,  39,  41,  63,  113,  160,  165 
(Evylaeus)  sp.,  62,  63 
(Lasioglossum)  sp.,  46 

pulzenus,  31,  36,  39,  44,  62,  64,  65,  66,  70, 
73,  75,  78,  79,  92 


Helianthus  annuus,  162,  185 

Heliopsis  levis,  187,  188 

Helix,  222 

Heracleum  lanatum,  106,  133,  148,  169 

Hesperis,  186 

Hieracium,  176,  240 

Hyacinthus,  136 

Hydrangea,  153 

Hyloicus  separatus,  55 

Ipomoea  purpurea,  147 

Jamesia  americana,  97 

Laciniaria  punctata,  217 
Lamium  album,  129,  132 
Lantana,  243 
Lathyrus,  133 

latifolius,  151 
Lavandula,  131 
Leucanthemum  vulgare,  162 
Leycesteria,  131 
Lilium  candidum,  165 
Linum  perenne,  165 
Linaria  vulgaris,  207 
Listera,  169 

Lobelia  erinus,  147,  169 
Lucilia,  157,  161 

caesar,  225,  226 
Lycaena,  16 

Macroglossa,  16,  153,  164,  165,  205,  206 

stellatarum,  136,  164,  190,  191,  192,  193 
Malva,  159,  175 

silvestris,  184 
Megachile  pugnata,  46 

wootoni,  34,  105,    106,    109,    145,    146,    148, 
149,  151,  154,  155,  156,  161,  165,  239 
Melampyrum  nemorosum,  132 
Melandrium,  162 
Melanostoma,  154 
Melissodes  fremonti,  71,  198 
Melolontha,  230 
Mentzelia,  57,  58,  92 
Mercurialis,  131 
Mertensia  alpina,  100,  101,  105,  106 

sibirica,  62,  63,  95,  98,  105 
Monarda  fistulosa,  79,  80,  81,  82,  85,  88,  89, 

91,  110,  115,  116,  117,  134,  239 
Monumetha  albifrons,  27,  34,  36,  39,  66 
Musca,  151,  156,  179 
Muscari  comosum,  175,  205 
Myosotis  alpestris,  151,  161 
Myrmica  ruginodis,  225 

Nicotiana,  148 

Odynerus,  150,  151 

Oenothera  biennis,  55,  131,  147,  210,  212,  217 

fruticosa,  55 

missouriensis,  55 

pinnatifida,  55 

speciosa,  165 
Osmia,  28,  30,  31,  40,  92,  113,  161,  181 

bruneri,  33,  34,  39,  70,  71,  73,  76 

californica,  48 

coloradella,  65 


INDEX. 


271 


Oamia — Continued. 
densa,  65,  68 
ferruginea,  222 

melanotricha,  65,  69,  70,  71,  72,  73 
phacelia,  65,  68,  69,  70,  71,  73,  75,  76,  105 
pentstemonis,  62,  65,  69,  70,  72,  73,  75,  76 

rufohirta,  222 
tricornis,  176 

Opulaster  opulifolius,  95,  97,  101,  104,  134 

Oxybelus,  151 

Paeonia,  181 

Papaver  orientalis,  159,  160,  161,  174,  18a 

rhoeas,  160,  171,  172,  184 
Papilio,  164 
Passiflora,  165 
Pedicularis  canadensis,  129 
Pelargonium  zonale,  149,  165,  166,  174,  196 
Pentstemon,  134 

barbatus,  100,  101,  106,  109,   112,  113,  114, 
115 

barbatus  labrosus,  68 

bridgesi,  68 

glaber,  78,  89,  111,  112,  113,  114 

glaucus,  111,  112,  114 

gracilis,  78,  111,  112,  113,  114,  115 

halli,  111,  112,  113,  114 

palmeri,  68 

secundiflorus,  78,  100,  101,  106,  109,  113,  115 

unilateralis,  112,  113,  114 
Perdita,  133 
Petunia,  147,  176,  240 

hybrida,  165 
Phlox  drummondi,  175 

paniculata,  149,  159,  164,  175,  192 
Pieris,  136.  137,  145,  146,  149,  153,  156,  161, 
163,  171,  181 

brassicae,  154,  191 
Pirus  communis,  194 
Pisum  sativum,  165 
Poa,  150 
Polistes  pallipes,  224 

gallicus,  141,  225 
Polygonum  convolvulus,  165 
Pompilus,  221 

scelestus,  233 
Portulaca  grandiflora,  196,  242 
Primula,  131,  136,  181 

Prosopis,  28,  37,  41,  92,   101,   105,   106,   113, 
161,  163,  165,  181 
elliptica,  34,  39,  73,  79 
episcopalis,  32,  33 
varifrons,  41,  66,  75 
Protoparce  quinquemaculata,  55 
Prunus  demissa,  28,  101,  134 

pennsylvanica,  28 
Pseudomasaris  vespoides,  39,  67,  68,  70,  71, 

77,  90,  101,  109 
Pulmonaria,  136,  243 
Pyrethrum  leucanthemum,  184 

Ranunculus,  130,  136 

acris,  171 
Ratibida,  217 
Reseda,  180 
Rheum  tataricum,  150 
Rhodocera,  153 

rhamni,  192 


Rhododendron  ciliatum,  179,  186 
Ribes,  138 

sanguineum,  150 

rubrum,  151 
Rosa,  18,  33,  34,  92,  95,  104,  105,  106,  109,  134 

acicularis,  101,  102,  134 

canina,  34 

rubiginosa,  34 
Rubus  deliciosus,  24,  28,  32,  33,  81,  89,  92, 
93,  95,  101,  134,  241 

strigosus,  32,  33,  62,  95,  97,  99,   101,   102, 
106,  134 
Rudbeckia,  157,  188,  241 

laciniata,  187,  217 
Rumex  obtusifolius,  150 

Salix,  131,  138 

Salvia  horminum,  153,  154,  155,  165,  181,  183, 
193 

splendens,  166 
Sarcophaga  vivipara,  225 
Saturnia  carpini,  225 
Saxifraga  umbrosa,  151 
Scabiosa,  130,  132,  149,  154 

atropurpurea,  161 
Scrophularia  nodosa,  100,  101,  106,  109,  115 
Secale,  150 

Selasphorus  platycercus,  63,  64,  74,  79 
Silpha  thoracica,  227,  230 
Solanum  rostratum,  217 
Solidago,  217 
Sphecodes  sp.,  64 
Sphex  vulgaris,  39 
Sphinx  convoluta,  189 
Stelis,  163 

Symphoricarpus  racemosus,  151,  167 
Symphytum  officinale,  184 
Syritta  pipiens,  178,  238,  240 
Systoechus  vulgaris,  74,  77 
Syrphus  americanus,  35,   129,   130,   137,   154. 
156,  191 

opinator,  38 

Tagetes,  147,  151 
Teucrium  chamaedrys,  137 

scorodonia,  137 
Thanaos  martialis,  23,  26,  76 
Tilia,  131 

Titusella  pronitens,  66,  74 
Tragopogon,  130 
Tremandra,  131 
Trichius,  136 
Trifolium,  132 
Tropaeolum,  131 

majus,  191 

Vanessa,  136,  145,  146,  161,  181 

Verbena,  192 

Veronica,  141 

Vespa  germanica,  27,  46,  62,  65,  69,  70,  71,  72, 

73,  76,  77,  141,  149,  150,  164,  165 
Vicia  americana,  129 

sepium,  132 
Viola,  136 

odorata,  161 
Volucella,  182 

Zinnia,  130,  154,  183 
elegans,  161,  181 


Descriptions  of  Plates. 

Plate  1.  Painted  flowers  of  Aconitum  and  Delphinium,  showing  experimental  method. 

Plate  2.  Life-history  of  flowers:  Aconitum  columbianum:  (1)  bud  opening;  (2)  4 
anthers  open;  (3)  8  anthers  open;  (4)  16  anthers  open;  (5)  4  anthers  whole; 
(6)  all  anthers  shed,  styles  visible;  (7)  carpels  enlarging,  stamens  shrunken; 
(8)  petals  falling.  Delphinium  scopulorum:  (9)  flower  just  open;  (10)  4 
anthers  shed;  (11)  8  anthers  shed;  (12)  16  anthers  shed;  (13)  4  anthers  whole; 
(14)  all  anthers  shed,  styles  visible;  (15)  carpels  enlarging,  stamens  shrunken; 
(16)  sepals  falling. 

Plate  3.  Life-history  of  flowers:  Rubus  strigosus:  (1)  bud  in  section;  (2)  bud  partly 
open;  (3)  flower  open,  upper  anthers  shedding;  (4)  sepals  flat,  petals  converg- 
ing, all  erect  anthers  shedding;  (5)  petals  erect,  stamens  mostly  shed,  con- 
verging; (6)  petals  flat,  stamens  brown;  (7)  petals  falling;  (8)  sepals  erect. 
Potentilla  arguta :  (9)  bud  cut,  stamens  converging;  (10)  flower  hah  open, 
stamens  erect,  stigmas  receptive;  (11)  petals  flat,  stamens  spreading;  (12) 
petals  ascending,  inner  stamens  erect;  (13)  all  stamens  shedding  and  con- 
verging; (14)  petals  fallen,  sepals  erect,  anthers  shrunken;  (15)  sepals  closed. 

Plate  4.  Life-history  of  flowers:  Heracleum  lanatum,  X6:  (1)  bud;  (2)  1  stamen  out; 
(3)  2  stamens  out;  (4)  3  stamens  out;  (5)  4  stamens  out;  (6)  all  stamens  out, 
erect,  mostly  shedding;  (7)  stamens  deflexed,  stigma  tips  visible;  (8)  stamens 
fallen,  styles  lengthened;  (9)  petals  falling,  styles  and  stylopodium  full-grown. 
Sedum  stenopetalum,  X6:  (10)  bud  in  section;  (11)  flower  half  open;  (12)  flower 
open,  inner  anthers  shedding;  (13)  inner  anthers  shed,  outer  shedding  carpels 
separating;  (14)  all  anthers  shed,  stigmas  receptive;  (15)  stamens  recurving, 
carpels  converging;  (16)  anthers  fallen,  filaments  ascending;  (17)  petals 
ascending,  drying. 

Plate  5.  Life-history  of  flowers:  Galium  boreale,  X10:  (1)  bud  in  section;  (2)  flower 
open,  stamens  erect,  shedding;  (3)  stamens  spreading,  anthers  shed;  (4)  sta- 
mens flat,  styles  receptive,  spreading;  (5)  stamens  deflexed,  stigmas  enlarged; 
(6)  corolla  withering,  style  elongated.  Saxifraga  bronchialis,  X4:  (7)  bud 
hanging;  (8)  bud  horizontal,  enlarged;  (9)  flower  open;  (10)  inner  row  of 
anthers  shedding;  (11)  inner  shed,  outer  shedding,  style  tips  recurved,  recep- 
tive; (12)  petals  and  anthers  fallen,  carpels  enlarging. 

Plate  6.  Life-history  of  flowers:  Campanula  rotundifolia,  Xl.5:  (1)  bud  in  section, 
erect;  (2)  bud  horizontal;  (3)  bud  hanging;  (4)  flower  half  open,  anthers 
shedding  on  style;  (5)  flower  open,  stamens  curling  downward,  style  dusted 
with  pollen;  (6)  anthers  separating,  stigmas  starting  to  recurve;  (7)  stigmas 
recurved,  receptive;  (8)  corolla  shriveling  and  drying.  Erysimum  asperum, 
X2:  (9)  bud  in  section;  (10)  stigma  protruding,  receptive,  petals  incurled; 
(11)  flower  opening,  4  upper  anthers  shedding;  (12)  flower  open,  upper  anthers 
recurving,  2  lower  shedding;  (13)  upper  anthers  shrunken,  lower  shed;  (14) 
lower'  anthers  shrinking,  petals  falling. 

Plate  7.  Life-history  of  flowers:  Geranium  caespitosum,  Xl.5:  (1)  bud  horizontal, 
corolla  tip  appearing;  (2)  bud  erect,  petals  separating;  (3)  flower  open;  (4) 
upper  anthers  shedding;  (5)  upper  shed,  lower  shedding;  (6)  anthers  mostly 
fallen;  (7)  styles  spread,  receptive;  (8)  petals  fallen,  pistil  enlarged.  Dode- 
catheon  meadia,  Xl.5:  (9)  bud  upright;  (10)  bud  hanging,  in  section;  (11) 
flower  half  open,  stigma  receptive,  anthers  swollen;  (12)  flower  fully  open, 
petals  reflexed,  anthers  shrinking;  (13)  flower  horizontal,  anthers  separating; 
(14)  flower  erect,  anthers  spread;  (15)  petals  shrunken  and  dried;  (16)  young 
pod  with  stigma  still  fresh. 

272 


DESCBIPTIONS  OF  PLATES.  273 

Plate  8.  Life-history  of  flowers:  Chamaenerium  angustifolium,  X2:  (1)  bud  hanging; 
(2)  bud  rising;  (3)  bud  in  section,  horizontal,  beginning  to  open;  (4)  flower 
open,  style  reflexed,  stamens  whole;  (5)  2  longer  stamens  shedding;  (6)  4 
longer  stamens  shedding,  style  hanging;  (7)  4  anthers  shrunken  and  4  shed- 
ding, stigma  lobes  spreading;  (8)  all  anthers  shrunken,  hanging,  stigma  lobes 
recurved,  receptive;  (9)  petals  closed,  stigma  projecting;  (10)  flower  withering. 

Plate  9.  Life-history  of  flowers:  Pachylophus  caespitosus,  XI:  (1)  bud  in  section,  an- 
thers shedding;  (2)  bud  opening,  stigma  lobes  protruding;  (3)  stigma  lobes 
separating;  (4)  stigma  lobes  horizontal;  (5)  flower  fully  open,  anthers  shed; 
(6)  petals  erect,  corolla  closing;  (7)  petals  withering,  bringing  anthers  against 
stigma  lobes;  (8)  corolla  wilted. 

Plate  10.  Life-history  of  flowers:  Pirola  ellipiica,  X2:  (1)  bud  in  section,  pores 
directed  inward;  (2)  flower  opening,  style  appearing,  straight,  pores  still 
closed  but  directed  downward;  (3)  pores  open,  downward,  style  curved, 
bringing  stigma  under  pores;  (4)  style  full  length,  curved  forward,  carpels 
enlarged,  petals  fallen.  Frasera  speciosa,  Xl.5:  (5)  bud  in  section;  (6)  flower 
half  open,  anthers  vertical,  introrse;  (7)  flower  open,  anthers  horizontal;  (8) 
anthers  extrorse;  (9)  1  anther  shedding;  (10)  2  opposite  anthers  shedding; 
(11)  3  anthers  shedding;  (12)  2  anthers  shedding  and  2  shed;  (13)  petals  erect, 
flower  half  closed;  (14)  flower  tightly  closed,  stamens  projecting.  Gentiana 
amarella,  X2:  (15)  bud  in  section,  stamens  introrse,  short;  (16)  bud  in  sec- 
tion, anthers  horizontal,  level  with  style;  (17)  anthers  extrorse,  shedding; 

(18)  anthers  shed,  stigmas  recurved;  (19)  flower  closed,  stigmas  closed,  pistil 
enlarged,  corolla  withering. 

Plate  11.  Life-history  of  flowers:  Gilia  aggregata,  Xl.5:  (1)  bud,  anthers  whole; 
(2)  bud,  anthers  shedding;  (3)  corolla  lobes  erect,  anthers  mostly  shed;  (4) 
lobes  spread,  style  elongated;  (5)  lobes  reflexed,  anthers  all  shed,  style  longer, 
stigmas  opening;  (6)  stigma  lobes  fully  spread,  receptive;  (7)  corolla  fallen, 
style  still  turgid.  Gilia  pinnatifida,  X3:  (8)  flower  half  open,  1  stamen  out; 
(9)  flower  open,  2  stamens  out;  (10)  3  stamens  out;  (11)  first  anther  shed;  (12) 
2  anthers  shed,  style  one-half  length;  (13)  3  anthers  shed,  style  two-thirds 
length;  (14)  all  anthers  shed,  style  full  length;  (15)  stamens  shrunken,  stig- 
mas turgid.  Mertensia  sibirica,  X2:  (16)  bud  in  section;  (17)  bud  partly 
open,  style  protruding,  receptive;  (18)  anthers  shedding,  style  elongating; 

(19)  style  as  long  as  corolla;  (20)  anthers  shed;  (21)  corolla  wilting  and  clos- 
ing, style  bent.  Lithospermum  multiftorum,  X2:  (22)  bud  in  section,  about 
two-thirds  grown;  (23)  flower  just  open,  anthers  shedding;  (24)  corolla  lobes 
spreading;  (25)  anthers  shed;  (26)  style  lengthening,  stigma  lobes  separating; 
(27)  corolla  fallen. 

Plate  12.  Life-history  of  flowers:  Pentstemon  glaber,  X2:  (1)  flower  just  open,  an- 
thers whole;  (2)  upper  pair  of  anthers  shedding;  (3)  upper  pair  shed,  lower 
shedding;  (4)  anthers  all  shed,  style  elongated;  (5)  stigma  curved  down- 
ward; (6)  corolla  fallen,  stigma  turgid;  (7)  longisection  of  stage  2;  (8)  longi- 
section  of  stage  5. 

Plate  13.  Life-history  of  flowers:  Castilleia  miniata,  X2:  (1)  corolla  in  calyx,  7  mm. 
long;  (2)  corolla  10  mm.  beginning  to  open;  (3)  corolla  15  mm.,  stigma 
protruding,  receptive;  (4)  outside  view  of  full-grown  calyx  with  stigma  ex- 
serted;  (5)  section  of  preceding;  (6)  style  3  mm.  long,  erect;  (7)  section  of 
preceding,  showing  the  pollen  mass;  (8)  corolla  full  length,  style  5  mm.  long; 
(9)  style  withering  at  tip;  (10)  style  reflexed,  corolla  withering.  Monarda 
fistulosa,  X2:  (11)  bud  in  section,  anthers  cracking;  (12)  flower  open,  anthers 
shedding;  (13)  stigma  projecting;  (14)  stamens  withering,  style  elongated, 
stigma  lobes  spread;  (15)  lower  lip  withering;  (16)  corolla  and  style  withering. 


274  EXPERIMENTAL  POLLINATION. 

Plate  14.  Life-history  of  flowers:  Allium  cernuum,  X3:  (1)  Bud  hanging,  cracking; 
(2)  bud  starting  to  ascend,  1  stamen  out;  (3)  bud  at  45  degrees,  perianth 
lobes  opening,  2  stamens  out,  1  anther  shedding;  (4)  3  stamens  out,  1  anther 
shedding,  and  1  shed;  (5)  5  stamens  out,  2  shed  and  1  shedding;  (6)  flower  hor- 
izontal, 5  anthers  shed;  (7)  flower  ascending,  style  elongating;  (8)  anthers 
falling,  style  exserted,  receptive;  (9)  anthers  fallen,  corolla  withering;  (10) 
style  shrunken,  corolla  withered.  Zygadenus  elegans,  X2:  (11)  flower  half 
open;  (12)  flower  open,  anthers  contiguous;  (13)  outer  row  of  anthers  spread 
and  shedding;  (14)  inner  row  of  anthers  spread  and  shedding;  (15)  anthers 
shed,  converging,  stigmas  beginning  to  spread;  (16)  anthers  fallen,  stigmas 
separated,  receptive;  (17)  petals  ascending,  pistil  enlarged;  (18)  petals 
erect,  keeled. 

Plate  15.  Mutilated  and  inverted  flowers  of  Aconitum,  XI. 

Plate  16.  Mutilated  flowers:  Aconitum  columbianum,  X1.5:  (1)  lower  sepals  re- 
moved; (2)  hood  removed;  (3)  perianth  removed;  (4)  hood  split  and  spread; 
(5)  hood  and  nectaries  removed;  (6)  side  petals  removed.  Delphinium 
scopidorum,  Xl.5:  (7)  normal  flower;  (8)  petals  removed;  (9)  side  sepals 
removed,  (10)  lower  sepals  removed;  (11)  spur  cut  off.  Monarda  fistulosa, 
X2:  (12)  lower  lip  cut  off;  (13)  upper  lip  cut  off;  (14)  both  lips  cut  off;  (15) 
lower  lip  split;  (16)  corolla  shortened;  (17)  upper  lip,  stamens  and  style  cut 
away. 

Plate  17.  Mutilated  flowers:  Geranium  caespitosum,  Xl.5:  (1)  petals  shortened  half; 
(2)  petals  trifid;  (3)  petals  removed.  Chamaenerium  angustifolium,  X2: 
(4)  petals  shortened  half;  (5)  petals  removed;  (6)  all  parts  removed  except 
pistil  and  nectary;  (7)  petals  and  sepals  removed;  (8)  flower  reduced  to  ovary 
and  nectary.  Pentstemon  glaber,  X2:  (9)  lower  lip  removed;  (10)  upper  lip 
removed;  (11)  both  lips  removed;  (12)  corolla  lobes  split. 


CLEMENTS  AND  LONG 


'    11 


F.<iith  S.  Clements  'hi. 


Life-history  of  the  flowers  of   Aconitum    columbianum  and    Delphinium 
scopulorwn. 


CLEMENTS  AND  LONG 


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Edith  S.  Clements  del. 

Life-history  of  the  flowers  of  Rubus  strigosus  and  Potentilla  gracilis 


CLEMENTS  AND  LONG 


Edith  S.  Clements  del. 

Life-history  of  the  flowers  of  Heracleum  lanatum  and  Sedum  stenopetalum. 


CLEMENTS  AND  LONG 


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7A  10 

'dith  S.  Clements  del. 

Life-history  of  the  flowers  of  Galium  boreale  and  Saxifraga  bronchialii 


CLEMENTS  AND  LONG 


Edith  S.  Clements  del. 

Life-history  of  the  flowers  of  Campanula  rotundifolia  and  Erysimum  asperum. 


CLEMENTS  AND  LONG 


Edith  S.  Clements  del. 

Life-history  of  the  flowers  of  Geranium  caespitosum  and  Dodecatheon meadia. 


CLEMENTS  AND  LONG 


Edith  S.  Clements  del. 

Life-history  of  the  flower  of  Chamaenerium  angustifolium. 


CLEMENTS  AND  LONG 


Edith  S.  Clements  del. 

Life-history  of  the  flower  of  Pachylophus  caespitosus 


CLLMLNTS  AND  LONG 


15  II  16 

Edith  S.  Clements  del. 

Life-history  of  the  flowers  of  Pirola  elliptica,  Frasera  speciosa,  and 
Gentiana  amarella. 


CLEMLNFS  AND  LONG 


r , 


Edith  S.  Clements  del. 


Life-history  of  the  flowers  of  Cilia  aggregata  and  pinnatifida,  Mertensia 
sibirica,  and  Lithospermum  multiflorum. 


Cl.f'.MENTS  AND  LONG 


,l,U,  S.  Clements  del. 


Life-history  of  the  flower  of  Pentstemon  glaber, 


CLEMENTS  AND  LONG 


.  J  '-  113  J 14 

Edith  S.  Clements  del. 

Life-history  of  the  flowers  of  Castilleia  miniata  and  Monarda  fistulosa. 


CLEMENTS  AND  LONG 


Edith  S.  Clements  del. 

Life-history  of  the  flowers  of  Alii  inn  cernuum  and  Zygadenus  elegans. 


CLEMENTS  AND  LONG 


I 


Edith  S.  Clements  del. 


Mutilated  and  inverted  flowers  of  Aconitum. 


CLEMENTS  AND  LONG 


13  \JU  j\:,  yi6 

Edith  S.  Clements  del. 

Mutilated  flowers  of  Aconitum,  Delphinium,  and  Monarda. 


CLEMENTS  AND  LONG 


11 

Mutilated  flowers  of  Geranium,  Chamaenerium,  and  Pentstemon  glaber. 


Edith  S.  Clements  del. 


florth  Carolina  State  Library 
Rala# 

■s.--:::T:.5^.s.::s-;5    M 


